Allow running generate_notices.generate_a_notice with workflow_dispatch

Author: andrewheard

.github/workflows/notice_generation.yml

@@ -11,7 +11,7 @@ on:
 jobs:
   generate_a_notice:
     # Don't run on private repo.
-    if: github.repository == 'Firebase/firebase-ios-sdk'
+    if: github.repository == 'Firebase/firebase-ios-sdk' || github.event_name == 'workflow_dispatch'
     runs-on: macos-14
     name: Generate NOTICES
     env: