Bump com.google.code.gson:gson from 2.8.6 to 2.8.9 in /github-plugin

Bumps [com.google.code.gson:gson](https://github.com/google/gson) from 2.8.6 to 2.8.9.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/main/CHANGELOG.md)
- [Commits](google/gson@gson-parent-2.8.6...gson-parent-2.8.9)

---
updated-dependencies:
- dependency-name: com.google.code.gson:gson
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

github-plugin/pom.xml

@@ -129,7 +129,7 @@ limitations under the License.
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
-      <version>2.8.6</version>
+      <version>2.8.9</version>
     </dependency>
     <dependency>
       <groupId>org.apache.httpcomponents</groupId>