add an optional PR number input for manual tip releases

needed for the future GitHub bot to track
comment-triggered PR builds

.github/workflows/release-tip.yml

@@ -4,7 +4,11 @@ on:
     types: [completed]
     branches: [main]
 
-  workflow_dispatch: {}
+  workflow_dispatch:
+    inputs:
+      pr:
+        type: number
+        required: false
 
 name: Release Tip