Merge branch 'cl/b4-cover-change-id' into next

The in-tree 'b4' cover letter template has been updated to include the
'change-id' trailer, ensuring that sent tags generated by 'b4' contain
the required tracking information for subsequent runs.

* cl/b4-cover-change-id:
  b4: include change-id in cover template

Author: gitster

.b4-cover-template

@@ -8,4 +8,5 @@ ${diffstat}
 ${range_diff}
 ---
 base-commit: ${base_commit}
+change-id: ${change_id}
 ${prerequisites}