[ci] Try to work around pkgconf installation failure. (#11836)

.github/workflows/main.yml

@@ -502,6 +502,7 @@ jobs:
           set -ex
           brew update
           brew uninstall --force pkg-config
+          brew install pkgconf --overwrite
           brew bundle --file=tests/Brewfile --no-upgrade
           cpanm IPC::System::Simple
           cpanm String::ShellQuote

extra/github-actions/build-mac.yml

@@ -8,6 +8,7 @@
     set -ex
     brew update
     brew uninstall --force pkg-config
+    brew install pkgconf --overwrite
     brew bundle --file=tests/Brewfile --no-upgrade
     cpanm IPC::System::Simple
     cpanm String::ShellQuote