ci(update): set "maintenance" label

Author: gr2m

.github/workflows/update.yml

@@ -53,6 +53,7 @@ jobs:
           branch: "openapi-update"
           commit-message: "WIP"
           author: "Octokit Bot <[email protected]>"
+          labels: "maintenance"
 
       # update pull request for dependabot update
       - name: Create Pull Request
@@ -75,3 +76,4 @@ jobs:
           branch: "${{ github.ref }}"
           commit-message: "WIP"
           author: "Octokit Bot <[email protected]>"
+          labels: "maintenance"