Fix macOS CI failure

[vasi]

We're getting errors because of homebrew's migration from pkg-config to pkgconf: Homebrew/homebrew-core#194885

To solve:

• Enable pkgconf in general, we'd prefer it to the ancient pkg-config
• For now, just wipe pkg-config from the macos running, and then update so we get the new pkgconf version that replaces it
• Eventually, Github will upgrade their runner so it has pkgconf, and we'll get to remove the brew remove/update

Error:

==> Pouring pkgconf--2.3.0_1.arm64_sonoma.bottle.tar.gz
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /opt/homebrew
Could not symlink bin/pkg-config
Target /opt/homebrew/bin/pkg-config
is a symlink belonging to pkg-config@0.29.2. You can unlink it:
  brew unlink pkg-config@0.29.2

To force the link and overwrite all conflicting files:
  brew link --overwrite pkgconf

To list all files that would be deleted:
  brew link --overwrite pkgconf --dry-run