Login into docker hub only when image push requried (#341)

.github/workflows/docker.yaml

@@ -16,12 +16,6 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Login to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
       - name: Build
         uses: docker/build-push-action@v6
         with:
@@ -38,6 +32,13 @@ jobs:
           echo "CREATE TABLE test_enc(id SERIAL, k INTEGER DEFAULT '0' NOT NULL, PRIMARY KEY (id)) USING pg_tde;" | docker run -e PGPASSWORD=mysecretpassword --rm postgres psql -h $IP -U postgres
           echo "SELECT * FROM test_enc;" | docker run -e PGPASSWORD=mysecretpassword --rm postgres psql -h $IP -U postgres
 
+      - name: Login to Docker Hub
+        if: ${{ github.ref == 'refs/heads/main' }}
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Push
         if: ${{ github.ref == 'refs/heads/main' }}
         uses: docker/build-push-action@v6