Use tolerance for objective bound tests

[blegat]

Without this PR, with Mosek, I get:

semiconttest: Test Failed at /home/blegat/.julia/dev/MathOptInterface/src/Test/intlinear.jl:810
  Expression: MOI.get(model, MOI.ObjectiveBound()) <= 3.0
   Evaluated: 3.0000000000000004 <= 3.0
Stacktrace:
 [1] _semitest(::MathOptInterface.Bridges.LazyBridgeOptimizer{MosekModel}, ::MathOptInterface.Test.TestConfig{Float64}, ::Bool) at /home/blegat/.julia/dev/MathOptInterface/src/Test/intlinear.jl:810
 [2] semiconttest(::MathOptInterface.Bridges.LazyBridgeOptimizer{MosekModel}, ::MathOptInterface.Test.TestConfig{Float64}) at /home/blegat/.julia/dev/MathOptInterface/src/Test/intlinear.jl:823
 [3] macro expansion at /home/blegat/.julia/dev/MathOptInterface/src/Test/config.jl:48 [inlined]
 [4] macro expansion at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Test/src/Test.jl:1115 [inlined]
 [5] intlineartest(::MathOptInterface.Bridges.LazyBridgeOptimizer{MosekModel}, ::MathOptInterface.Test.TestConfig{Float64}, ::Array{String,1}) at /home/blegat/.julia/dev/MathOptInterface/src/Test/config.jl:48