Bump org.apache.maven.plugins:maven-site-plugin in /org.jacoco.build

Bumps [org.apache.maven.plugins:maven-site-plugin](https://github.com/apache/maven-site-plugin) from 3.12.1 to 3.21.0.
- [Release notes](https://github.com/apache/maven-site-plugin/releases)
- [Commits](https://github.com/apache/maven-site-plugin/compare/maven-site-plugin-3.12.1...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] <support@github.com>

org.jacoco.build/pom.xml

diff --git a/org.jacoco.build/pom.xml b/org.jacoco.build/pom.xml
index f5f451e..74930f1 100644
--- a/org.jacoco.build/pom.xml
+++ b/org.jacoco.build/pom.xml
@@ -403,7 +403,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-site-plugin</artifactId>
-          <version>3.12.1</version>
+          <version>3.21.0</version>
         </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>