ci: Downgrade Qt on MacOS from Qt6 to Qt5

.github/workflows/macos.yml

@@ -25,7 +25,7 @@ jobs:
     - run: |
         python -m pip install --upgrade pip
         python -m pip install pytest pytest-xdist jsonschema
-    - run: brew install pkg-config ninja llvm qt
+    - run: brew install pkg-config ninja llvm qt@5
     - env:
         CPPFLAGS: "-I/usr/local/include"
         LDFLAGS: "-L/usr/local/lib"
@@ -33,7 +33,8 @@ jobs:
         # These cannot evaluate anything, so we cannot set PATH or SDKROOT here
       run: |
         export SDKROOT="$(xcodebuild -version -sdk macosx Path)"
-        export PATH="$HOME/tools:/usr/local/opt/qt/bin:$PATH:$(brew --prefix llvm)/bin"
+        export PATH="$HOME/tools:/usr/local/opt/qt@5/bin:$PATH:$(brew --prefix llvm)/bin"
+        export PKG_CONFIG_PATH="/usr/local/opt/qt@5/lib/pkgconfig:$PKG_CONFIG_PATH"
         ./run_unittests.py
 
   project-tests-appleclang:
@@ -45,7 +46,7 @@ jobs:
     - uses: actions/checkout@v2
     # use python3 from homebrew because it is a valid framework, unlike the actions one:
     # https://github.com/actions/setup-python/issues/58
-    - run: brew install pkg-config ninja llvm qt boost ldc hdf5 openmpi lapack scalapack sdl2 python3
+    - run: brew install pkg-config ninja llvm qt@5 boost ldc hdf5 openmpi lapack scalapack sdl2 python3
     - run: |
         python3 -m pip install --upgrade setuptools
         python3 -m pip install --upgrade pip
@@ -58,7 +59,8 @@ jobs:
         # These cannot evaluate anything, so we cannot set PATH or SDKROOT here
       run: |
         export SDKROOT="$(xcodebuild -version -sdk macosx Path)"
-        export PATH="$HOME/tools:/usr/local/opt/qt/bin:$PATH:$(brew --prefix llvm)/bin"
+        export PATH="$HOME/tools:/usr/local/opt/qt@5/bin:$PATH:$(brew --prefix llvm)/bin"
+        export PKG_CONFIG_PATH="/usr/local/opt/qt@5/lib/pkgconfig:$PKG_CONFIG_PATH"
         ./run_project_tests.py --backend=ninja
 
   Qt4macos: