Improve sync process (#4)

* Fix versions / security issues #3 and #4

* v4 and allow manual dispatch

.github/workflows/sync-from-reddit.yml

@@ -1,6 +1,7 @@
 name: Sync from Reddit
 
 on:
+  workflow_dispatch:
   schedule:
     # run hourly at some arbitrary minute
     - cron: 3 * * * *
@@ -10,7 +11,7 @@ jobs:
     name: Sync from Reddit
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Configure git user
         run: |
           git config user.name 'github-actions[bot]'