ci/github-script/bot: handle deleted maintainer accounts gracefully

When a maintainer deletes their GitHub account, the bot would crash with a 404 error when trying to fetch their user info via `/user/{id}`.

This caused the scheduled bot workflow to fail repeatedly until manual intervention (e.g., closing/reopening the affected PR to clear the requested reviewer).

Fix by returning null from getUser() for 404 responses and filtering out null users when building the reviewers list.

ci/github-script/bot.js

@@ -133,6 +133,11 @@ module.exports = async ({ github, context, core, dry }) => {
           id,
         })
         .then((resp) => resp.data)
+        .catch((e) => {
+          // User may have deleted their account
+          if (e.status === 404) return null
+          throw e
+        })
     }
 
     return users[id]

ci/github-script/reviewers.js

@@ -42,9 +42,15 @@ async function handleReviewers({
   }
 
   const users = new Set([
-    ...(await Promise.all(
-      maintainers.map(async (id) => (await getUser(id)).login.toLowerCase()),
-    )),
+    ...(
+      await Promise.all(
+        maintainers.map(async (id) => {
+          const user = await getUser(id)
+          // User may have deleted their account
+          return user?.login?.toLowerCase()
+        }),
+      )
+    ).filter(Boolean),
     ...owners
       .filter((handle) => handle && !handle.includes('/'))
       .map((handle) => handle.toLowerCase()),