allow running GitHub workflow manually (commons-app#5248)

Author: mnalis

.github/workflows/android.yml

@@ -1,6 +1,6 @@
 name: Android CI
 
-on: [push, pull_request]
+on: [push, pull_request, workflow_dispatch]
 
 concurrency:
   group: build-${{ github.event.pull_request.number || github.ref }}