explicitly install Qt 5.15.0 via install-qt-action@v3 for MacOS brew …

…build

.github/workflows/qctools.yml

@@ -13,6 +13,8 @@ jobs:
           - compiler: clang-9
             packages: llvm@13
             env: { 'CC': 'clang', 'CXX': 'clang++' }
+          - qt_version: "5.15.0"
+            qt_modules: "qtmultimedia"
 
     runs-on: macos-latest
 
@@ -37,10 +39,16 @@ jobs:
       run: |
         brew install ${{ matrix.packages }} pkg-config ffmpeg
 
+    - name: Install Qt5
+      uses: jurplel/install-qt-action@v3
+      with:
+        version: ${{ matrix.qt_version }}
+        modules: ${{ matrix.qt_modules }}
+
     - name: Install qwt-qt5
       run: |
         wget https://raw.githubusercontent.com/Homebrew/homebrew-core/56cd02e96876d1fb5b9ae951d605585fe8d614de/Formula/qwt.rb
-        brew install ./qwt.rb
+        brew install --ignore-dependencies ./qwt.rb
 
     - name: Set Qt5 environment path
       run: |