Update dependencies in pom.xml

Bump the parent POM version from 10.2.0 to 10.4.0 and add a specific
version (6.0.0) for the plugin-util-api dependency.

Author: uhafner

pom.xml

@@ -99,6 +99,8 @@
     <dependency>
       <groupId>io.jenkins.plugins</groupId>
       <artifactId>plugin-util-api</artifactId>
+      <!-- TODO: remove the version when a matching BOM is available -->
+      <version>6.0.0</version>
       <classifier>tests</classifier>
       <scope>test</scope>
     </dependency>