Add TagBot lookback to match latest PkgTemplates

Author: iamed2

.github/workflows/TagBot.yml

@@ -4,6 +4,9 @@ on:
     types:
       - created
   workflow_dispatch:
+    inputs:
+      lookback:
+        default: 3
 jobs:
   TagBot:
     if: github.event_name == 'workflow_dispatch' || github.actor == 'JuliaTagBot'