Add a type annotation and descriptive comment for UNSUPPORTED_COMBINATIONS

[HsuehYi]

What changes were proposed in this pull request?

This PR adds proper type annotations to UNSUPPORTED_COMBINATIONS in python/pyspark/install.py

Why are the changes needed?

Changes improve type checking.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Errors on install.py before Changes (delete # type: ignore):

starting mypy annotations test...
annotations failed mypy checks:
python/pyspark/install.py:38: error: Need type annotation for "UNSUPPORTED_COMBINATIONS" (hint: "UNSUPPORTED_COMBINATIONS: list[<type>]

After changes:
Verified with mypy that install.py has no type errors

Was this patch authored or co-authored using generative AI tooling?

No.

[bearomorphism]

I'm already fixing the issue: #59343

[gaogaotiantian]

#59343 is favored for this specific issue.