gh-36737: Fix `make SPKG-uninstall` for Python packages after #36452
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#36452 broke `make SPKG-uninstall` for Python packages.
Reproducer:
```
$ make zipp-uninstall
...
if [ -d '/Users/mkoeppe/s/sage/sage-rebasing/worktree-
clean/local/var/lib/sage/venv-python3.10' ]; then sage-spkg-uninstall
zipp '/Users/mkoeppe/s/sage/sage-rebasing/worktree-
clean/local/var/lib/sage/venv-python3.10'; fi
Uninstalling existing 'zipp'
Running pip-uninstall script for 'zipp'
ERROR: Could not open requirements file: [Errno 2] No such file or
directory: '/Users/mkoeppe/s/sage/sage-rebasing/worktree-
clean/local/var/lib/sage/venv-python3.10/var/lib/sage/scripts/zipp/spkg-
requirements.txt'
Warning: pip exited with status 0
Removing stamp file '/Users/mkoeppe/s/sage/sage-rebasing/worktree-
clean/local/var/lib/sage/venv-
python3.10/var/lib/sage/installed/zipp-3.11.0'
$ ./sage -pip list | grep zipp
zipp 3.11.0
```
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### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/36737
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee
