BUG: Unstack/pivot raising ValueError on large result
- [x] closes #26314
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

thanks @mroeschke  @mroeschke this seems to significantly increase the run time running the tests locally.

also the tests fail with pytest-xdist... node down. > @mroeschke this seems to significantly increase the run time running the tests locally.
> 
> also the tests fail with pytest-xdist... node down.

Addressed in https://github.com/pandas-dev/pandas/pull/45112. Now takes ~4 seconds locally.