Be able to trigger manually this workflow.

Author: bmarty

.github/workflows/sync-from-external-sources.yml

@@ -1,5 +1,6 @@
 name: Sync Data From External Sources
 on:
+  workflow_dispatch:
   schedule:
     # At 00:00 on every Monday UTC
     - cron: '0 0 * * 1'
@@ -80,4 +81,4 @@ jobs:
 
             *Note*: Change are coming from [this project](https://github.com/matrix-org/matrix-analytics-events)
           branch: sync-analytics-plan
-          base: develop
+          base: develop