Add a workflow to set milestone for a merged PR automatically (#14084)

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# Description
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Add a workflow to set milestone for a merged PR automatically.

A example action run log looks like:
https://github.com/hustcer/milestone-action/actions/runs/11320750633/job/31478761283


[`hustcer/milestone-action`](https://github.com/hustcer/milestone-action)
is a Github action powered by `nushell`, and still in active
development, so I will use `main` branch for easily to try new changes

.github/workflows/milestone.yml

@@ -0,0 +1,18 @@
+# Description:
+#   - Update milestone of a merged PR
+
+name: Milestone Action
+on:
+  pull_request_target:
+    types: [closed]
+
+jobs:
+  update-milestone:
+    runs-on: ubuntu-latest
+    name: Milestone Update
+    if: ${{github.event.pull_request.merged == true}}
+    steps:
+      - name: Set Milestone
+        uses: hustcer/milestone-action@main
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}