chore(deps): bump maven-plugin-plugin 3.7.1 -> 3.15.2

The 'report' goal was moved out of maven-plugin-plugin into a separate
maven-plugin-report-plugin starting in 3.15. The project does not run
'mvn site' anywhere (no scripts/, .buildkite/, or pom.xml invocations),
so the report output was already unused; drop the goal rather than add
a new plugin just to host it.

Resolves the build failure that blocked Dependabot PR #2313 (and the
group bumps before it). Verified locally with mvn install on the
mockserver-maven-plugin module — BUILD SUCCESS.

Author: jamesdbloom

mockserver/mockserver-maven-plugin/pom.xml

@@ -360,15 +360,17 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-plugin-plugin</artifactId>
-                <version>3.7.1</version>
+                <version>3.15.2</version>
                 <configuration>
                     <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>
                 </configuration>
                 <executions>
                     <execution>
                         <goals>
                             <goal>descriptor</goal>
-                            <goal>report</goal>
+                            <!-- 'report' goal moved to maven-plugin-report-plugin in
+                                 maven-plugin-plugin 3.15+; the project does not run
+                                 'mvn site' so the report output is unused — drop it. -->
                             <goal>addPluginArtifactMetadata</goal>
                             <goal>helpmojo</goal>
                         </goals>