change username in pipeline

.gitea/workflows/docker-build.yml

@@ -13,7 +13,7 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: g.eliaskohout.de
-          username: ${{ secrets.USERNAME }}
+          username: ${{ gitea.actor }}
           password: ${{ secrets.ACCESS_TOKEN }}
 
       - name: Set up Docker Buildx