ExUnit: Raise explaining what failed on invalid tags

[eksperimental]

Errors were a bit cryptic when running mix test.

@tag "a" before:

== Compilation error in file test/ex_unit_tag_error_test.exs ==
** (FunctionClauseError) no function clause matching in anonymous fn/2 in ExUnit.Case.normalize_tags/1

    The following arguments were given to anonymous fn/2 in ExUnit.Case.normalize_tags/1:

        # 1
        "a"

        # 2
        %{}

    (ex_unit 1.18.4) lib/ex_unit/case.ex:896: anonymous fn/2 in ExUnit.Case.normalize_tags/1
    (elixir 1.18.4) lib/enum.ex:2546: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_unit 1.18.4) lib/ex_unit/case.ex:669: ExUnit.Case.register_test/6
    test/ex_unit_tag_error_test.exs:7: (module)
    (elixir 1.18.4) lib/kernel/parallel_compiler.ex:542: Kernel.ParallelCompiler.require_file/2
    (elixir 1.18.4) lib/kernel/parallel_compiler.ex:425: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8

@tag "a" now:

== Compilation error in file test/ex_unit_tag_error_test.exs ==
** (RuntimeError) an invalid value for a tag was used; expected an atom or a keyword list, got: "a"
    (ex_unit 1.20.0-dev) lib/ex_unit/case.ex:953: anonymous fn/2 in ExUnit.Case.normalize_tags/1
    (elixir 1.20.0-dev) lib/enum.ex:2580: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_unit 1.20.0-dev) lib/ex_unit/case.ex:715: ExUnit.Case.register_test/6
    test/ex_unit_tag_error_test.exs:7: (module)
    (elixir 1.20.0-dev) lib/kernel/parallel_compiler.ex:599: Kernel.ParallelCompiler.require_file/2
    (elixir 1.20.0-dev) lib/kernel/parallel_compiler.ex:482: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8

@tag [:foo, :bar] before:

== Compilation error in file test/ex_unit_tag_error_test.exs ==
** (ArgumentError) argument error
    (stdlib 6.2) :maps.from_list([:foo, :bar])
    (elixir 1.18.4) lib/enum.ex:1543: Enum.into_map/1
    (elixir 1.18.4) lib/enum.ex:2546: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_unit 1.18.4) lib/ex_unit/case.ex:669: ExUnit.Case.register_test/6
    test/ex_unit_tag_error_test.exs:7: (module)
    (elixir 1.18.4) lib/kernel/parallel_compiler.ex:542: Kernel.ParallelCompiler.require_file/2
    (elixir 1.18.4) lib/kernel/parallel_compiler.ex:425: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8

@tag [:foo, :bar] now:

== Compilation error in file test/ex_unit_tag_error_test.exs ==
** (RuntimeError) an invalid value for a tag was used; expected an atom or a keyword list, got: [:foo, :bar]
    (ex_unit 1.20.0-dev) lib/ex_unit/case.ex:953: anonymous fn/2 in ExUnit.Case.normalize_tags/1
    (elixir 1.20.0-dev) lib/enum.ex:2580: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_unit 1.20.0-dev) lib/ex_unit/case.ex:715: ExUnit.Case.register_test/6
    test/ex_unit_tag_error_test.exs:7: (module)
    (elixir 1.20.0-dev) lib/kernel/parallel_compiler.ex:599: Kernel.ParallelCompiler.require_file/2
    (elixir 1.20.0-dev) lib/kernel/parallel_compiler.ex:482: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8

[sabiwara]

💜

[josevalim]

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