ci: Push to Dockerhub as well when building a release

.github/workflows/github_release.yml

@@ -101,6 +101,11 @@ jobs:
         uses: docker/setup-qemu-action@v1
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: griefed
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v1
         with:
@@ -117,3 +122,5 @@ jobs:
           tags: |
             ghcr.io/griefed/ltt-mapmaker:latest
             ghcr.io/griefed/ltt-mapmaker:${{ steps.tag.outputs.tag }}
+            griefed/ltt-mapmaker:latest
+            griefed/ltt-mapmaker:${{ steps.tag.outputs.tag }}