Bump maven-pmd-plugin from 3.8 to 3.15.0

Bumps [maven-pmd-plugin](https://github.com/apache/maven-pmd-plugin) from 3.8 to 3.15.0.
- [Release notes](https://github.com/apache/maven-pmd-plugin/releases)
- [Commits](apache/maven-pmd-plugin@maven-pmd-plugin-3.8...maven-pmd-plugin-3.15.0)

---
updated-dependencies:
- dependency-name: org.apache.maven.plugins:maven-pmd-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -24,7 +24,7 @@
         <checkstyle.version>2.17</checkstyle.version>
         <findbugs.version>3.0.5</findbugs.version>
         <javadoc.version>3.0.0</javadoc.version>
-        <pmd.version>3.8</pmd.version>
+        <pmd.version>3.15.0</pmd.version>
         <jdepend.version>2.0</jdepend.version>
         <javancss.version>2.1</javancss.version>
         <project.info.version>2.9</project.info.version>