Update the TagBot workflow.

Update TagBot to be compatible with changes to GitHub actions. See the
following link for more information:

    https://discourse.julialang.org/t/ann-required-updates-to-tagbot-yml/49249

Author: kernelmethod

.github/workflows/TagBot.yml

@@ -1,10 +1,13 @@
 name: TagBot
 on:
-  schedule:
-    - cron: 0 * * * *
+  issue_comment:
+    types:
+      - created
+  workflow_dispatch:
 jobs:
   TagBot:
     runs-on: ubuntu-latest
+    if: github.event_name == 'workflow_dispatch' || github.actor == 'JuliaTagBot'
     steps:
       - uses: JuliaRegistries/TagBot@v1
         with: