Add pull_request to the list of events that don't need refs.

README.md

@@ -75,7 +75,7 @@ Configure this action by either inlining these options in your workflow file or
 | `allow-ghsas`         | Contains a list of GitHub Advisory Database IDs that can be skipped during detection.                                                                                             | Any GHSAs from the [GitHub Advisory Database](https://github.com/advisories)             | none          |
 | `license-check`       | Enable or disable the license check performed by the action.                                                                                                                                | `true`, `false`                                                                          | `true`       |
 | `vulnerability-check` | Enable or disable the vulnerability check performed by the action.                                                                                                                          | `true`, `false`                                                                          | `true`       |
-| `base-ref`/`head-ref` | Provide custom git references for the git base/head when performing the comparison check. This is only used for event types other than `pull_request_target`.                     | Any valid git ref(s) in your project                                                     | none          |
+| `base-ref`/`head-ref` | Provide custom git references for the git base/head when performing the comparison check. This is only used for event types other than `pull_request` and `pull_request_target`.  | Any valid git ref(s) in your project                                                     | none          |
 
 *not supported for use with GitHub Enterprise Server