Update actions/cache action to v6

Author: xdev-renovate

.github/workflows/check-build.yml

@@ -48,7 +48,7 @@ jobs:
           ${{ runner.os }}-mvn-build-
 
     - name: Cache Vaadin prod bundles
-      uses: actions/cache@v5
+      uses: actions/cache@v6
       with:
         path: |
           **/bundles/prod.bundle