Bump org.jenkins-ci.plugins:plugin from 5.5 to 5.9 (#433)

Author: dependabot[bot]

pom.xml

@@ -28,7 +28,7 @@
     <parent>
         <groupId>org.jenkins-ci.plugins</groupId>
         <artifactId>plugin</artifactId>
-        <version>5.5</version>
+        <version>5.9</version>
         <relativePath/>
     </parent>
     <groupId>org.jenkins-ci.plugins.workflow</groupId>