Bump org.apache.maven.plugins:maven-site-plugin from 3.20.0 to 3.21.0 (#1048)

Author: dependabot[bot]

pom.xml

@@ -100,7 +100,7 @@
     <maven-project-info-reports-plugin.version>3.8.0</maven-project-info-reports-plugin.version>
     <maven-release-plugin.version>3.1.1</maven-release-plugin.version>
     <maven-resources-plugin.version>3.3.1</maven-resources-plugin.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>
     <maven-war-plugin.version>3.4.0</maven-war-plugin.version>