pkg-config: attempt to mitigate issue on github runners

[mseri]

This will not fix the issue completely unfortunately.

Problem

On homebrew the package pkg-config has been replaced by pkgconf, the executable pkg-config is now a symlink to pkgconf. On GitHub macos runner, pkg-config comes preinstalled and conflicts with the installation of the new package pkgconf, making the CIs fail:

::error::Cannot install pkgconf because conflicting formulae are installed.%0A  pkg-config: because both install `pkg.m4` file%0A%0APlease `brew unlink pkg-config` before continuing.%0A%0AUnlinking removes a formula's symlinks from /opt/homebrew. You can%0Alink the formula again after the install finishes. You can `--force` this%0Ainstall, but the build may fail or cause obscure side effects in the%0Aresulting software.%0A
            brew install pkgconf

Moreover, if pkg-config is uninstalled and pkgconf is manually installed, it seems that the symlink to pkg-config that is installed with it is not executable (at least it cannot be found by opam).

Current Solutions

The only solutions, currently, are to either force the installation of conf-pkg-config.2 on macos which uses the old name for the depext, or execute brew unlink pkg-config; brew install pkgconf; brew unlink pkgconf; brew link pkg-config; before installing anything.

UPDATE: there is another solution (see #26891 (comment)) that is running brew update; brew upgrade; brew install pkgconf beforehand

This change

Not changing the package name in the depext, means that the package is broken on any new installation on macos with homebrew, while changing it means that it is broken on GitHub runners. This new version should install fine on both cases, provided that the GitHub runners unlink or remove the old package beforehand: brew uninstall pkg-config. It does not guarantee that pkg-config is a working executable though, that is either a bug in homebrew or in the GitHub runners that we have no control over.

See also the discussions in #26891

[mseri]

This will not solve the issue, we just need to wait for macos runners in github to be updated: actions/runner-images#10984