fix: remove default value from assignees

Author: vineetbavniya-cd

.github/workflows/pr-auto-assignee.yml

@@ -8,7 +8,6 @@ on:
         description: 'A list of assignees(GitHub user name) to be added to PR'
         required: true
         type: string
-        default: true
       reviewers:
         description: 'A list of reviewers(GitHub user name) to be added to PRs'
         required: false

docs/pr-auto-assignee.md

@@ -10,7 +10,7 @@ This workflow can be used to automatically assign assignees to a PR when it is o
 | Name              | Description                                           | Required | Type    |
 | ----------------- | ----------------------------------------------------- | -------- | ------- |
 | `assignees`       | List of GitHub usernames to randomly assign to the PR | No       | String  |
-| `assign_yourself` | Whether to assign the PR creator as an assignee       | Yes      | Boolean |
+| `assign_yourself` | Whether to assign the PR creator as an assignee       | No      | Boolean |