feat(gradle): login to Docker Hub if credentials are provided

...because this may be needed if testcontainers tests are included.
Testcontainers will pick up the docker login in case it needs to pull
images based on the configure image pull policy.

.github/workflows/gradle-library.yml

@@ -109,6 +109,20 @@ jobs:
           # fetch-depth 0 is required to fetch all tags (and to determine the version based on tags)
           fetch-depth: ${{ inputs.publish-tasks != '' && '0' || '1' }}
 
+      #
+      # Login to Docker Hub
+      #
+      # May be required for pulling images for testcontainers
+      #
+      - name: Login to DockerHub
+        if: env.DOCKER_HUB_USERNAME
+        uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
+        with:
+          username: ${{ secrets.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_PASSWORD }}
+        env:
+          DOCKER_HUB_USERNAME: ${{ secrets.DOCKER_HUB_USERNAME }}
+
       #
       # Build, test and create Docker image
       #

.github/workflows/gradle-service.yml

@@ -125,6 +125,20 @@ jobs:
             done
           fi
 
+      #
+      # Login to Docker Hub
+      #
+      # May be required for pulling images for testcontainers
+      #
+      - name: Login to DockerHub
+        if: env.DOCKER_HUB_USERNAME
+        uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
+        with:
+          username: ${{ secrets.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_PASSWORD }}
+        env:
+          DOCKER_HUB_USERNAME: ${{ secrets.DOCKER_HUB_USERNAME }}
+
       #
       # Build, test and create Docker image
       #