Update dependency mysql:mysql-connector-java to v8.0.31

Author: renovate[bot]

build.gradle

@@ -47,7 +47,7 @@ ext {
     googleInjectGuiceVersion = '5.1.0'
     clivernKangarooVersion = '0.0.1'
     tinylogVersion = '2.4.1'
-    mysqlConnectorVersion = '8.0.28'
+    mysqlConnectorVersion = '8.0.31'
     hibernateVersion = '5.6.5.Final'
 }