Update build action to create docker tag on PRs

.github/workflows/build.yml

@@ -4,22 +4,33 @@ name: Build
 on:
   release:
     types: [published]
+  pull_request:
 
 jobs:
   docker-image:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
 
-      - name: Extract tag name
-        id: vars
+      - name: Extract tag name for release
+        if: ${{ github.event_name == 'release' }}
+        id: vars-release
         run: echo "tag=${GITHUB_REF#refs/*/}" >> $GITHUB_OUTPUT
 
+      - name: Extract tag name for PR
+        if: ${{ github.event_name != 'release' }}
+        id: vars-pr
+        run: |
+          TAG=${GITHUB_HEAD_REF//\/\#/-}
+          TAG=${TAG//\//-}
+          TAG=${TAG//\#/-}
+          echo "tag=$TAG" >> $GITHUB_OUTPUT
+
       - name: Build and publish docker image
         uses: docker/[email protected]
         with:
           repository: faforever/faf-python-server
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
-          build_args: GITHUB_REF=${{ steps.vars.outputs.tag }}
+          build_args: GITHUB_REF=${{ steps.vars-release.outputs.tag || steps.vars-pr.outputs.tag }}
           tag_with_ref: true