fix up as review comments

Signed-off-by: Sam Yuan <[email protected]>

.github/workflows/build-push.yml

@@ -5,7 +5,25 @@ on:
     branches: [ main ]
 
 jobs:
+
+  changes:
+    runs-on: ubuntu-latest
+    outputs:
+      src: ${{ steps.changes.outputs.src }}
+      infra: ${{ steps.changes.outputs.infra }}
+    steps:
+    - uses: actions/checkout@v3
+    - uses: dorny/paths-filter@v2
+      id: changes
+      with:
+        filters: |
+          src:
+            - 'dockerfiles/requirements.txt'
+            - 'dockerfiles/Dockerfile.base'
+
   buildbase:
+    needs: changes
+    if: ${{ needs.changes.outputs.src == 'true' }}
     runs-on: ubuntu-latest
     steps:
     - name: checkout