CI: Updated version of macos image
- [x] closes #31281
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Will #30990 work after this change?

does ```gcc``` support macos 10.15? Hmm though looks like the macOS build is stuck in queued > Hmm though looks like the macOS build is stuck in queued

@WillAyd Not anymore, I guess it was downloading the image or refreshing the cache. seems reasonable