chore: fix version in docker publish workflow (@fehmer) (monkeytypegame#6339)

Author: fehmer

.github/workflows/publish-docker-images.yml

@@ -49,7 +49,7 @@ jobs:
           tags: ${{ env.BE_REPO }}:latest,${{ steps.bemeta.outputs.tags }}
           labels: ${{ steps.bemeta.outputs.labels }}
           build-args: |
-            server_version: {{version}}
+            server_version: ${{ github.event.release.tag_name }}
 
       - name: Backend publish description
         uses: peter-evans/dockerhub-description@e98e4d1628a5f3be2be7c231e50981aee98723ae