Update maven.version to v3.9.9

Author: renovate[bot]

pom.xml

@@ -108,7 +108,7 @@
     <mariadb-client.version>3.5.3</mariadb-client.version>
     <maven-plugin-sisu.version>0.3.5</maven-plugin-sisu.version>
     <maven-shared-utils.version>3.4.2</maven-shared-utils.version>
-    <maven.version>3.8.8</maven.version>
+    <maven.version>3.9.9</maven.version>
     <plexus-utils.version>3.6.0</plexus-utils.version>
     <plugin-dockerfile.version>0.46.0</plugin-dockerfile.version>
     <plugin-exec.version>3.5.0</plugin-exec.version>