Speed up a test
Saves 30s of test time, it ain't much but it's honest work :-) Also moves a magic number to a constant.

- [ ] closes #xxxx (Replace xxxx with the Github issue number)
- [ ] [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 an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

thanks @jonashaag all for faster tests, but we also cannot change them like this (which doesn't really test much). I basically am always -1 on monkey patching as it 99% of the time doesnt' catch anything. Actually my version of the test fails before the #8621 fix, I double checked. So it actually tests the bug, just with a smaller number 