Bump org.jenkins-ci.plugins:plugin from 5.5 to 5.6 (#373)

Author: dependabot[bot]

pom.xml

@@ -28,7 +28,7 @@
     <parent>
         <groupId>org.jenkins-ci.plugins</groupId>
         <artifactId>plugin</artifactId>
-        <version>5.5</version>
+        <version>5.6</version>
         <relativePath />
     </parent>