macos-13 builds are failing

[JelleZijlstra]

Bug report

In both #105511 and #116025, the macos-13 builds fail with:

Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink bin/2to3
Target /usr/local/bin/2to3
already exists. You may want to remove it:
  rm '/usr/local/bin/2to3'

To force the link and overwrite all conflicting files:
  brew link --overwrite python@3.12

To list all files that would be deleted:
  brew link --overwrite python@3.12 --dry-run

The failure first appears on the main branch after #115661 was merged, but that looks unlikely to be related, especially since the failure happens before we even start building CPython. I suspect something changed in the runner.

Linked PRs

• gh-116026: Try disabling rebuilds of dependents in Homebrew #116027
• [3.11] gh-116026: Try disabling rebuilds of dependents in Homebrew (GH-116027) #116157
• [3.12] gh-116026: Try disabling rebuilds of dependents in Homebrew (GH-116027) #116158

[JelleZijlstra]

Comparing a successful run (https://github.com/python/cpython/actions/runs/8065615837/job/22031816546) and a failing one (https://github.com/python/cpython/actions/runs/8073964044/job/22058540805), I noticed that in the successful run we didn't do anything to xz, but in the failing run we decided to upgrade from 5.4.5 to 5.4.6. That upgrade then makes Homebrew reinstall Python 3.12 for some reason (because Python depends on xz?), and that leads to the brew link error.

As a workaround, I opened a PR to pin xz to 5.4.5.