DOC: Documentation for MultiIndex.get_locs() is missing in v0.25 docs
Like a comment in #30056. I add "get_locs" to method

- [ ] closes #30056
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
