Bump maven-pmd-plugin from 3.20.0 to 3.21.0

Bumps [maven-pmd-plugin](https://github.com/apache/maven-pmd-plugin) from 3.20.0 to 3.21.0.
- [Release notes](https://github.com/apache/maven-pmd-plugin/releases)
- [Commits](apache/maven-pmd-plugin@maven-pmd-plugin-3.20.0...maven-pmd-plugin-3.21.0)

---
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>

Author: dependabot[bot]

pom.xml

@@ -109,7 +109,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-pmd-plugin</artifactId>
-                <version>3.20.0</version>
+                <version>3.21.0</version>
                 <configuration>
                     <format>csv</format>
                     <linkXRef>true</linkXRef>