feat(ci): Run cron jobs on workflow dispatch (#15316)

Author: ncooke3

.github/workflows/common_cocoapods_cron.yml

@@ -48,9 +48,9 @@ on:
 
 jobs:
   cron-job:
-    # This job is intended to be run on a schedule, on the main repo.
-    if: github.event_name == 'schedule' && github.repository == 'Firebase/firebase-ios-sdk'
-
+    if: |
+      github.repository == 'firebase/firebase-ios-sdk' && \
+      (github.event_name == 'schedule' || github.event_name == 'workflow_dispatch')
     runs-on: ${{ inputs.runs_on }}
     strategy:
       matrix: