use trigger to run tagbot instead of cron (#197)

* use trigger to run tagbot instead of cron

* Update .github/workflows/TagBot.yml

Co-authored-by: Milan Bouchet-Valat <[email protected]>

Co-authored-by: Milan Bouchet-Valat <[email protected]>

Author: kleinschmidt

.github/workflows/TagBot.yml

@@ -1,9 +1,11 @@
 name: TagBot
 on:
-  schedule:
-    - cron: 0 * * * *
+  issue_comment:
+    types:
+      - created
 jobs:
   TagBot:
+    if: github.event_name == 'workflow_dispatch' || github.actor == 'JuliaTagBot'
     runs-on: ubuntu-latest
     steps:
       - uses: JuliaRegistries/TagBot@v1