TST: show_versions test with unmerged commits
- [x] closes #32120
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Closing pending investigation in #32120. Re-opened, the issue wasnt with un-merged commits, but with git worktree.  re-using versioneer code handles the problem. gentle ping @simonjayhawkins @WillAyd ; this is workflow-affecting OK thanks @jbrockmendel 

Heads up - I’m at CZI this week so may be slow to respond to some of your other PRs. Should catch up over the weekend at the latest