Restore maven plugin version.
<!-- Jenkins Plug-in Dependencies Versions -->
<autograding.version>3.3.1</autograding.version>
<git-forensics.version>1.2.1</git-forensics.version>
+ <jenkins-maven-plugin.version>3.8</jenkins-maven-plugin.version>
<antisamy-markup-formatter.version>2.1</antisamy-markup-formatter.version>
<job-dsl.version>1.78.1</job-dsl.version>
<flexible-publish.version>0.15.2</flexible-publish.version>
<dependency>
<groupId>org.jenkins-ci.main</groupId>
<artifactId>maven-plugin</artifactId>
+ <version>${jenkins-maven-plugin.version}</version>
<scope>test</scope>
<exclusions>
<exclusion>
