Regression: CI tests fail on master due to serialization code changes

[fingolfin]

See e.g. here.

Free Associative Algebra over Rational Coefficients: Error During Test at /home/runner/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:9
  Got exception outside of a @test
  MethodError: no method matching load_object(::Oscar.DeserializerState, ::Type{Oscar.FreeAssAlgIdeal}, ::Vector{Any}, ::AbstractAlgebra.Generic.FreeAssAlgebra{QQFieldElem})
  Closest candidates are:
    load_object(::Oscar.DeserializerState, ::Type{var"#s3169"} where var"#s3169"<:Hecke.QuadSpace, ::Vector{T} where T, ::Any) at /home/runner/work/Oscar.jl/Oscar.jl/src/Serialization/QuadForm.jl:26
    load_object(::Oscar.DeserializerState, ::Type{var"#s3169"} where var"#s3169"<:Union{Oscar.Laurent.LaurentMPolyIdeal, Oscar.FreeAssAlgIdeal, MPolyIdeal}, ::Vector{T} where T, ::Vector{T} where T) at /home/runner/work/Oscar.jl/Oscar.jl/src/Serialization/Rings.jl:286
    load_object(::Oscar.DeserializerState, ::Type{var"#s3169"} where var"#s3169"<:Union{RingElem, FreeAssAlgElem, MatElem}, ::Vector{Any}, ::Union{Ring, FreeAssAlgebra, MatSpace}) at /home/runner/work/Oscar.jl/Oscar.jl/src/Serialization/Rings.jl:65
    ...
  Stacktrace:
    [1] load_object(s::Oscar.DeserializerState, T::Type{Oscar.FreeAssAlgIdeal}, gen_terms::Vector{Any}, params::Vector{Any})
      @ Oscar ~/work/Oscar.jl/Oscar.jl/src/Serialization/Rings.jl:288
    [2] load_typed_object(s::Oscar.DeserializerState, dict::Dict{Symbol, Any}; override_params::Nothing)
      @ Oscar ~/work/Oscar.jl/Oscar.jl/src/Serialization/main.jl:262
    [3] load(io::IOStream; params::Nothing, type::Nothing)
      @ Oscar ~/work/Oscar.jl/Oscar.jl/src/Serialization/main.jl:511
    [4] #6702
      @ ~/work/Oscar.jl/Oscar.jl/src/Serialization/main.jl:516 [inlined]
    [5] open(f::Oscar.var"#6702#6703"{Nothing, Nothing}, args::String; kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
      @ Base ./io.jl:330
    [6] open
      @ ./io.jl:328 [inlined]
    [7] #load#6701
      @ ~/work/Oscar.jl/Oscar.jl/src/Serialization/main.jl:515 [inlined]
    [8] test_save_load_roundtrip(func::var"#1496#1499"{Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{QQFieldElem}}}, path::String, original::Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{QQFieldElem}}; params::Nothing)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/basic_types.jl:5
    [9] test_save_load_roundtrip(func::Function, path::String, original::Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{QQFieldElem}})
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/basic_types.jl:3
   [10] macro expansion
      @ ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:19 [inlined]
   [11] macro expansion
      @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Test/src/Test.jl:1151 [inlined]
   [12] (::var"#1494#1497")(path::String)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:10
   [13] mktempdir(fn::var"#1494#1497", parent::String; prefix::String)
      @ Base.Filesystem ./file.jl:729
   [14] mktempdir(fn::Function, parent::String) (repeats 2 times)
    [8] test_save_load_roundtrip(func::var"#1496#1499"{Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{ZZRingElem}}}, path::String, original::Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{ZZRingElem}}; params::Nothing)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/basic_types.jl:5
    [9] test_save_load_roundtrip(func::Function, path::String, original::Oscar.FreeAssAlgIdeal{AbstractAlgebra.Generic.FreeAssAlgElem{ZZRingElem}})
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/basic_types.jl:3
   [10] macro expansion
      @ ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:19 [inlined]
   [11] macro expansion
      @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Test/src/Test.jl:1151 [inlined]
   [12] (::var"#1494#1497")(path::String)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:10
   [13] mktempdir(fn::var"#1494#1497", parent::String; prefix::String)
      @ Base.Filesystem ./file.jl:729
   [14] mktempdir(fn::Function, parent::String) (repeats 2 times)
      @ Base.Filesystem ./file.jl:727
   [15] macro expansion
      @ ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:7 [inlined]
   [16] macro expansion
      @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Test/src/Test.jl:1151 [inlined]
   [17] top-level scope
      @ ~/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:7
   [18] include
      @ ./Base.jl:385 [inlined]
   [19] macro expansion
      @ ./timing.jl:368 [inlined]
   [20] include(str::String)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/runtests.jl:76
   [21] top-level scope
      @ ~/work/Oscar.jl/Oscar.jl/test/Serialization/runtests.jl:8
   [22] include
      @ ./Base.jl:385 [inlined]
   [23] macro expansion
      @ ./timing.jl:368 [inlined]
   [24] include(str::String)
      @ Main ~/work/Oscar.jl/Oscar.jl/test/runtests.jl:76
   [25] (::Base.var"#834#839"{typeof(include)})(r::Base.RefValue{Any}, args::Tuple{String})
      @ Base ./asyncmap.jl:100
   [26] macro expansion
      @ ./asyncmap.jl:234 [inlined]
   [27] (::Base.var"#850#851"{Base.var"#834#839"{typeof(include)}, Channel{Any}, Nothing})()
      @ Base ./task.jl:417
Test Summary:                                         | Pass  Error  Total
Serialization.Algebras                                |   12      2     14
  Free Associative Algebra over Rational Coefficients |    6      1      7
  Free Associative Algebra over Integers Coefficients |    6      1      7
ERROR: LoadError: LoadError: LoadError: Some tests did not pass: 12 passed, 0 failed, 2 errored, 0 broken.
in expression starting at /home/runner/work/Oscar.jl/Oscar.jl/test/Serialization/Algebras.jl:6
in expression starting at /home/runner/work/Oscar.jl/Oscar.jl/test/Serialization/runtests.jl:8
in expression starting at /home/runner/work/Oscar.jl/Oscar.jl/test/runtests.jl:154
ERROR: LoadError: Package Oscar errored during testing