gh-141174: Improve ForwardRef test coverage

[dr-carlos]

All lines in the ForwardRef class (except _evaluate) should now be covered by tests, except

cpython/Lib/annotationlib.py

Lines 146 to 147 in 42d0140

	elif callable(owner):
	globals = getattr(owner, "__globals__", None)

I couldn't think of a useful test for those lines that wouldn't involve using the undocumented ForwardRef constructor (as the owner is automatically applied by annotationlib.get_annotations()).

• Issue: annotationlib: Improve test coverage #141174