ci: add 3.x docker tag

.github/workflows/docker.yml

@@ -45,6 +45,7 @@ jobs:
           tags: |
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}.x
             type=raw,value=latest,enable={{is_default_branch}}
 
       - name: Build and push Docker images
@@ -56,4 +57,4 @@ jobs:
           tags: ${{ steps.meta.outputs.tags }}
           platforms: linux/amd64,linux/arm64,linux/arm/v7
           cache-from: type=gha
-          cache-to: type=gha,mode=max
+          cache-to: type=gha,mode=max