Adding Manual Trigger for mainline and staging public sync (#489)

* Update sync-staging.yaml

* Update sync-mainline.yaml

.github/workflows/sync-mainline.yaml

@@ -1,6 +1,7 @@
 name: Sync amd-mainline to public repository
 
 on:
+  workflow_dispatch:
   push:
     branches: [ amd-mainline ]
 

.github/workflows/sync-staging.yaml

@@ -1,6 +1,7 @@
 name: Sync amd-staging to public repository
 
 on:
+  workflow_dispatch:
   push:
     branches: [ amd-staging ]