Skip steps individually instead of bailing out

`exit 0` does not bail out early it seems: https://github.com/matrix-org/rust-synapse-compress-state/actions/runs/16961790179/job/48076133728

We have to individually skip every step instead.

Author: anoadragon453

.github/workflows/docker.yaml

@@ -39,26 +39,23 @@ jobs:
             type=semver,pattern=v{{version}}
             type=semver,pattern=v{{major}}.{{minor}}
 
-      - name: Don't push to registry if this is a PR
-        if: github.event_name == 'pull_request'
-        run: |
-          echo "Not pushing the image to any container registry as this workflow is running on a pull request"
-          exit 0
-
       - name: Log in to DockerHub
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v2
         with:
           username: ${{ secrets.DOCKER_HUB_USERNAME }}
           password: ${{ secrets.DOCKER_HUB_TOKEN }}
 
       - name: Log in to GHCR
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v2
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push all platforms
+        if: github.event_name != 'pull_request'
         uses: docker/build-push-action@v4
         with:
           push: true