gh-96197: Add del sys.breakpointhook behavior test

[youknowone]

• Issue: del sys.breakpointhook is not tested in test_builtin #96197

[corona10]

I would like to check PyPy's behavior also.

[youknowone]

Python 3.9.12 (05fbe3aa5b0845e6c37239768aa455451aa5faba, Mar 29 2022, 09:54:47)
[PyPy 7.3.9 with GCC Apple LLVM 13.0.0 (clang-1300.0.29.30)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>> import sys
>>>> del sys.breakpointhook 
>>>> breakpoint()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: lost sys.breakpointhook
>>>> 

I think this is not a part to leave as implementation details. Debugging tools will expect a single way to check problems across multiple python versions.

[corona10]

I think this is not a part to leave as implementation details.

This could be. I needed to check what's happening on PyPy when we del the sys.breakpointhook.
But looks like the same behavior.

[corona10]

lgtm

[youknowone]

It could be, but it should not be. This is a sort of external api