Deprecate conflicting @testset arguments

[mhauru]

Currently @testset allows specifying multiple descriptions and testset types, and only the last one will take effect. The others will be silently ignored.

This PR starts printing deprecation warnings whenever such conflicting arguments are provided.

Ideally I would also propose fixing the order in which the arguments must be provided (currently order doesn't matter), but I've left that out at least for now since that's a more breaking change. Can put it in though if others are for it.

[fingolfin]

I really like the idea, thank you!

Unfortunately the tests in here don't seem to work as intended? At least they cause the CI tests to fail:

Error During Test at /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1734
  Test threw exception
  Expression: #= /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1734 =# @macroexpand #= /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1734 =# @testset("name1", "name2", begin
        end)
  Multiple descriptions provided to @testset. This may be disallowed in the future.
  Stacktrace:
    [1] _depwarn(msg::Any, funcsym::Any, force::Bool)
      @ Base ./deprecated.jl:241
...
Error During Test at /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1737
  Test threw exception
  Expression: #= /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1737 =# @macroexpand #= /cache/build/tester-amdci4-12/julialang/julia-master/julia-33da5bdd9b/share/julia/stdlib/v1.12/Test/test/runtests.jl:1737 =# @testset(DefaultTestSet, DefaultTestSet, begin
        end)
  Multiple testset types provided to @testset. This may be disallowed in the future.

[LilithHafner]

This is a great idea; definitely worth implementing. CI currently fails because we run tests with --depwarn=error, so these warnings via Base.depwarn are errors instead. Quick exploration locally seems to indicate the implementation is good.

[mhauru]

Tests pass for me locally indeed without --depwarn=error. I can convert the @test_logs calls to @test_throws and try to get tests to pass that way.

[LilithHafner]

Then Base.runtests() will fail unless --depwarn=error is set which will pass CI, but be bad for folks doing manual testing.

You're looking for @test_deprecated

[LilithHafner]

Thank you! I appreciate this deprecation.