Beautify mergify (#434) (#446)

Author: mergify[bot]

.github/mergify.yml

@@ -7,6 +7,9 @@ pull_request_rules:
       backport:
         branches:
           - humble
+        labels:
+          - humble
+        title: Backport of {{ title }} (#{{ number }}) to {{ destination_branch }}
 
   - name: backport to galactic at reviewers discretion
     conditions:
@@ -16,6 +19,9 @@ pull_request_rules:
       backport:
         branches:
           - galactic
+        labels:
+          - galactic
+        title: Backport of {{ title }} (#{{ number }}) to {{ destination_branch }}
 
   - name: backport to foxy at reviewers discretion
     conditions:
@@ -25,6 +31,9 @@ pull_request_rules:
       backport:
         branches:
           - foxy
+        labels:
+          - foxy
+        title: Backport of {{ title }} (#{{ number }}) to {{ destination_branch }}
 
   - name: ask to resolve conflict
     conditions: