fixup! Install with tests extra

Author: hugovk

.github/workflows/test-mingw.yml

@@ -78,7 +78,7 @@ jobs:
           pushd depends && ./install_extra_test_images.sh && popd
 
       - name: Build Pillow
-        run: CFLAGS="-coverage" python3 -m pip install .
+        run: CFLAGS="-coverage" python3 -m pip install .[tests]
 
       - name: Test Pillow
         run: |