ci/github-script/reviewers: improve "needs: reviewers" label

This should fix the bug where the "needs: reviewer" label was set too
early, just to be removed immediately, because reviewers were then
requested.

ci/github-script/bot.js

@@ -375,7 +375,10 @@ module.exports = async ({ github, context, core, dry }) => {
       })
 
       if (!pull_request.draft) {
-        await handleReviewers({
+        // We set this label earlier already, but the current PR state can be very different
+        // after handleReviewers has requested reviews, so update it in this case to prevent
+        // this label from flip-flopping.
+        prLabels['9.needs: reviewer'] = await handleReviewers({
           github,
           context,
           core,

ci/github-script/reviewers.js

@@ -68,7 +68,8 @@ async function handleReviewers({
     log(
       `Too many reviewers (${reviewers.join(', ')}), skipping review requests.`,
     )
-    return
+    // false indicates, that we do have reviewers and don't need the "needs: reviewers" label.
+    return false
   }
 
   const requested_reviewers = new Set(
@@ -113,6 +114,13 @@ async function handleReviewers({
       reviewers,
     })
   }
+
+  // Return a boolean on whether the "needs: reviewers" label should be set.
+  return (
+    new_reviewers.size === 0 &&
+    existing_reviewers.size === 0 &&
+    requested_reviewers.size === 0
+  )
 }
 
 module.exports = {