Add `frozendict` test in `Lib/test/test_crossinterp.py`

[sobolevn]

Currectly there are plans to add special handling of frozendict to subinterpreters. #148234

While it is not implemented, we should test that frozendict just works in Lib/test/test_crossinterp.py. Especially given that 3.15 feature freeze is coming soon.

I have a PR ready :)

Linked PRs

• gh-149219: Test frozendict in Lib/test/test_crossinterp.py #149220