ci(workflow): simplify docker buildx installation

Replace separate `docker buildx install` step with installing `docker-buildx` package directly via apk, streamlining the Docker Buildx setup in the CI workflow.

.gitea/workflows/build.yml

@@ -118,8 +118,7 @@ jobs:
 
       - name: Set up Docker Buildx
         run: |
-          apk add --no-cache docker-cli docker-cli-compose
-          docker buildx install
+          apk add --no-cache docker-cli docker-cli-compose docker-buildx
 
       - name: Login to registry
         run: echo "${{ secrets.REG_TOKEN }}" | docker login "${{ secrets.REGISTRY }}" -u "${{ secrets.REG_USER }}" --password-stdin