Add rstrip in def _strip_extras

[mtsokol]

Hi All,

Installing from .whl file with extras, where there's a whitespace between filename and extras section is broken:

bash-3.2$ pip install '/tmp/array_record/all_dist/array_record.whl [beam]'
ERROR: Invalid requirement: '/tmp/array_record/all_dist/array_record.whl [beam]': Expected package name at the start of dependency specifier
    /tmp/array_record/all_dist/array_record.whl [beam]
    ^
Hint: It looks like a path. File '/tmp/array_record/all_dist/array_record.whl [beam]' does not exist.

which is caused by untrimmed file extension: .whl instead of .whl.

This PR fixes it by striping path when separating from extras section, with a test that fails for the current main.

[notatallshaw]

Hi @mtsokol thanks for your PR to pip, please be aware it may take a bit for a maintainer to review as we are all doing this on a volunteer basis.