fix: older API versions have different attributes for bots

"user": {
  ...
  "login": "dependabot[bot]",
  "type": "Bot",
  ...
}

src/action.js

@@ -19,7 +19,7 @@ async function run() {
 
   if (
     (!assignees || assignees.length === 0) &&
-    !author.is_bot
+    (!author.is_bot || author.type !== 'Bot')
   ) {
     await client.request(
       `POST /repos/${owner}/${repo}/issues/${issue_number}/assignees`,