BUG: to_datetime with mixed-string-and-numeric
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Surfaced while implementing #55564
Thanks @jbrockmendel  @jbrockmendel mind taking a look at this test failure on main? This PR _might_ have been responsible https://github.com/pandas-dev/pandas/actions/runs/6728530133/job/18288031590 will do Reverting this doesn't seem to fix the problem, but it definitely seems connected to what ive been doing the last few days.  i'll keep trying to track this down
 Thanks! i dont think a measured-in-minutes fix is forthcoming.  might need to xfail or comment-out that offending line