Bump org.apache.maven.plugins:maven-site-plugin from 3.20.0 to 3.21.0

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

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

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -144,7 +144,7 @@
     <maven-project-info-reports-plugin.version>3.7.0</maven-project-info-reports-plugin.version>
     <maven-resources-plugin.version>3.3.1</maven-resources-plugin.version>
     <maven-shared-utils.version>3.4.2</maven-shared-utils.version>
-    <maven-site-plugin.version>3.20.0</maven-site-plugin.version>
+    <maven-site-plugin.version>3.21.0</maven-site-plugin.version>
     <maven-source-plugin.version>3.3.1</maven-source-plugin.version>
     <maven-surefire-plugin.version>3.5.1</maven-surefire-plugin.version>
     <nexus-staging-maven-plugin.version>1.7.0</nexus-staging-maven-plugin.version>