Bump org.apache.maven.plugins:maven-site-plugin from 3.7.1 to 3.21.0

Bumps [org.apache.maven.plugins:maven-site-plugin](https://github.com/apache/maven-site-plugin) from 3.7.1 to 3.21.0.
- [Release notes](https://github.com/apache/maven-site-plugin/releases)
- [Commits](apache/maven-site-plugin@maven-site-plugin-3.7.1...maven-site-plugin-3.21.0)

---
updated-dependencies:
- dependency-name: org.apache.maven.plugins:maven-site-plugin
  dependency-version: 3.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pom.xml

@@ -1085,7 +1085,7 @@
     <version.plugin.maven.jxr>3.6.0</version.plugin.maven.jxr>
     <version.plugin.maven.release>3.1.1</version.plugin.maven.release>
     <version.plugin.maven.resources>3.3.1</version.plugin.maven.resources>
-    <version.plugin.maven.site>3.7.1</version.plugin.maven.site>
+    <version.plugin.maven.site>3.21.0</version.plugin.maven.site>
     <version.plugin.maven.source>3.3.1</version.plugin.maven.source>
     <version.plugin.maven.surefire>3.5.4</version.plugin.maven.surefire>
     <version.plugin.mojo.build-helper>3.6.1</version.plugin.mojo.build-helper>