Bump Maven Stapler plugin from 1.19 to 1.20 (#608)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pom.xml

@@ -70,10 +70,10 @@
 
     <!-- Filled in by "maven-hpi-plugin" with the path to "org-netbeans-insane-hook.jar" extracted from "jenkins-test-harness" -->
     <jenkins.insaneHook />
-    <jenkins-test-harness.version>1834.v91a_a_5f4b_6529</jenkins-test-harness.version>
+    <jenkins-test-harness.version>1837.vb_6efb_1790942</jenkins-test-harness.version>
 
     <hpi-plugin.version>3.34</hpi-plugin.version>
-    <stapler-plugin.version>1.19</stapler-plugin.version>
+    <stapler-plugin.version>1.20</stapler-plugin.version>
 
     <!-- Defines a SpotBugs threshold. Use "Low" to discover low-priority bugs.
          Hint: SpotBugs considers some real NPE risks in Jenkins as low-priority issues, it is recommended to enable it in plugins.
@@ -747,7 +747,6 @@
       <plugin>
         <groupId>org.kohsuke.stapler</groupId>
         <artifactId>maven-stapler-plugin</artifactId>
-        <extensions>true</extensions>
       </plugin>
       <plugin>
         <artifactId>maven-release-plugin</artifactId>