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] <support@github.com>

Author: dependabot[bot]

pom.xml

@@ -108,7 +108,7 @@
 				<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
 				<plugin>
 					<artifactId>maven-site-plugin</artifactId>
-					<version>3.7.1</version>
+					<version>3.21.0</version>
 				</plugin>
 				<plugin>
 					<artifactId>maven-project-info-reports-plugin</artifactId>