make workflow shareable accross repos. (#1304)

Author: n-g

.github/workflows/require-reviewers.yaml

@@ -1,4 +1,4 @@
-name: PRs requirements
+name: PR requirements
 on:
   pull_request:
     types:
@@ -9,6 +9,9 @@ on:
       - review_request_removed
       - auto_merge_enabled
 
+  # Allow calling sharing this workflow with other repositories.
+  workflow_call:
+
 jobs:
   require-reviewer:
     runs-on: nscloud