chore: add manual dispatch option to issue reprioritization manager (#…

…21044)

This allows us to manually run the action when we want, especially in situations where the weekly run failed.

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.github/workflows/issue-reprioritization.yml

@@ -1,5 +1,6 @@
 name: issue-reprioritization
-on: 
+on:
+  workflow_dispatch: {}
   schedule:
     - cron: "0 0 * * 0"