CI: run on all three: ubuntu-latest, macos-latest, windows-latest

.github/workflows/tests.yml

@@ -12,10 +12,11 @@ on:
 
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
         # pick lower and upper versions only
         python-version: ["3.9", "3.12"]
 
@@ -33,15 +34,16 @@ jobs:
         uses: modflowpy/install-modflow-action@v1
 
       - name: Install dependencies
-        shell: bash
         run: |
           python -m pip install pip --upgrade --disable-pip-version-check
-          echo "$HOME/.local/bin" >> $GITHUB_PATH
           pip install -e .[test]
 
       - name: Run tests with required packages
-        run: |
-          pytest -v --cov
+        run: pytest -v --cov
+
+      - name: Install PyQt5 for macOS
+        if: matrix.os == 'macos-latest'
+        run: pip install PyQt5
 
       - name: Run tests with optional packages
         run: |