Fix building on macOS in CI

The original hack no longer works as Homebrew installs to /opt/homebrew
by default for ARM [1], and hosted macOS runners on GitHub now uses ARM
by default [2].

While I'm at it, I replaced the hack with a more general solution. It's
inspired by other Homebrew formulae that use cmake and qt@5 [3].

[1] https://docs.brew.sh/Installation
[2] https://github.com/actions/runner-images?tab=readme-ov-file#available-images
[3] https://github.com/search?q=repo%3AHomebrew%2Fhomebrew-core+CMAKE_PREFIX_PATH+qt%405&type=code

.github/workflows/ci.yml

@@ -39,12 +39,8 @@ jobs:
           brew update
           brew install libchewing qt@5
 
-          # Qt
-          brew link --force qt@5
-          # Homebrew does not link mkspecs and plugins https://github.com/Homebrew/homebrew-core/issues/93056
-          export HOMEBREW_QT5_VERSION=$(brew list --versions qt@5 | rev | cut -d' ' -f1 | rev)
-          sudo ln -s /usr/local/Cellar/qt@5/$HOMEBREW_QT5_VERSION/mkspecs /usr/local/mkspecs
-          sudo ln -s /usr/local/Cellar/qt@5/$HOMEBREW_QT5_VERSION/plugins /usr/local/plugins
+          # Allow CMake to find qt@5 by passing down the environment variable
+          echo "CMAKE_PREFIX_PATH=$(brew --prefix qt@5)" >> $GITHUB_ENV
       if: ${{ matrix.os == 'macos-latest' }}
 
     - name: Configure CMake