change clang to 21 to match QtCreator

Author: Salanto

.github/workflows/main.yml

@@ -20,7 +20,7 @@ jobs:
     - name: Run clang-format style check.
       uses: jidicula/clang-format-action@v4.5.0
       with:
-        clang-format-version: '14'
+        clang-format-version: '21'
         check-path: '.'
 
   build-linux: