ci: Update GitHub Actions workflow to use github.event_name for build conditions

Author: paul-gauthier

.github/workflows/docker-build-test.yml

@@ -36,14 +36,14 @@ jobs:
       uses: docker/setup-buildx-action@v3
 
     - name: Login to DockerHub
-      if: ${{ secrets.DOCKERHUB_USERNAME != '' }}
+      if: ${{ github.event_name != 'pull_request' }}
       uses: docker/login-action@v3
       with:
         username: ${{ secrets.DOCKERHUB_USERNAME }}
         password: ${{ secrets.DOCKERHUB_PASSWORD }}
 
     - name: Build Docker images (PR)
-      if: ${{ secrets.DOCKERHUB_USERNAME == '' }}
+      if: ${{ github.event_name == 'pull_request' }}
       uses: docker/build-push-action@v5
       with:
         context: .
@@ -53,7 +53,7 @@ jobs:
         target: aider
 
     - name: Build Docker images (Push)
-      if: ${{ secrets.DOCKERHUB_USERNAME != '' }}
+      if: ${{ github.event_name != 'pull_request' }}
       uses: docker/build-push-action@v5
       with:
         context: .
@@ -64,7 +64,7 @@ jobs:
         target: aider
 
     - name: Build Docker full image (PR)
-      if: ${{ secrets.DOCKERHUB_USERNAME == '' }}
+      if: ${{ github.event_name == 'pull_request' }}
       uses: docker/build-push-action@v5
       with:
         context: .
@@ -74,7 +74,7 @@ jobs:
         target: aider-full
 
     - name: Build Docker full image (Push)
-      if: ${{ secrets.DOCKERHUB_USERNAME != '' }}
+      if: ${{ github.event_name != 'pull_request' }}
       uses: docker/build-push-action@v5
       with:
         context: .