Replace chart-testing with git diff

Signed-off-by: Ivan Polchenko <2119240+i5okie@users.noreply.github.com>

.github/workflows/on_push_main.yaml

@@ -79,15 +79,13 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Set up chart-testing
-        uses: helm/chart-testing-action@v2.6.1
-
-      - name: Run chart-testing (list-changed)
+      - name: Check for chart changes
         id: list-changed
         run: |
-          changed=$(ct list-changed --target-branch ${{ github.event.repository.default_branch }})
-          if [[ -n "$changed" ]]; then
+          if git diff --name-only ${{ github.event.before }} ${{ github.sha }} | grep -q "^charts/"; then
             echo "changed=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=false" >> "$GITHUB_OUTPUT"
           fi
 
   update_configs_repo: