Merge pull request #1545 from ucb-bar/check-label

Bump mergify to check label

.mergify.yml

@@ -22,3 +22,21 @@ pull_request_rules:
     actions:
       label:
         add: [Backport]
+
+  - name: check PR has changelog label
+    conditions:
+      - base=main
+    actions:
+      post_check:
+        success_conditions:
+          - "label~=^changelog:"
+        title: |
+          {% if check_succeed %}
+          Labeled for changelog
+          {% else %}
+          Needs label for changelog
+          {% endif %}
+        summary: |
+          {% if not check_succeed %}
+          Your pull request must have a changelog label (e.g. `changelog: ...`).
+          {% endif %}