Added trigger cron workflow for RestrictedActions branch sync

we're having problems with the restricted action getting disabled due to repo inactivity,
so it's best we trigger it from here, since this repo's activity is what it's
interested in anyway.

.github/workflows/branch-sync-cron-trigger.yml

@@ -0,0 +1,32 @@
+#Since GitHub automatically disables cron actions after 60 days of repo inactivity, we need the active repo (PM)
+#to trigger the branch merge workflow explicitly. This avoids the need for TOS-violating actions which we previously
+#used to keep the restricted action active, as the workflow depends on the activity of this repo anyway.
+
+name: Trigger branch sync
+
+on:
+  schedule:
+    - cron: "0 0 * * *" #once per day so we don't spam merge commits on busy days
+  workflow_dispatch: #for testing
+
+jobs:
+  trigger:
+    name: Trigger branch sync RestrictedActions workflow
+    runs-on: ubuntu-22.04
+
+    steps:
+      - name: Generate access token
+        id: generate-token
+        uses: actions/create-github-app-token@v2
+        with:
+          app-id: ${{ vars.RESTRICTED_ACTIONS_DISPATCH_ID }}
+          private-key: ${{ secrets.RESTRICTED_ACTIONS_DISPATCH_KEY }}
+          owner: ${{ github.repository_owner }}
+          repositories: RestrictedActions
+
+      - name: Dispatch branch sync restricted action
+        uses: peter-evans/repository-dispatch@v3
+        with:
+          token: ${{ steps.generate-token.outputs.token }}
+          repository: ${{ github.repository_owner }}/RestrictedActions
+          event-type: pocketmine_mp_branch_sync