Bump mysql-connector-java from 8.0.15 to 8.0.18

Bumps [mysql-connector-java](https://github.com/mysql/mysql-connector-j) from 8.0.15 to 8.0.18.
- [Release notes](https://github.com/mysql/mysql-connector-j/releases)
- [Changelog](https://github.com/mysql/mysql-connector-j/blob/release/8.0/CHANGES)
- [Commits](https://github.com/mysql/mysql-connector-j/compare/8.0.15...8.0.18)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

build.gradle

@@ -69,7 +69,7 @@ ext {
         "dm"                         : fileTree(dir: 'libs', includes: ["jdbcDriver-18.jar"]),
         "kingbase"                   : fileTree(dir: 'libs', includes: ["kingbase8-8.2.0.jar"]),
         "h2"                         : "com.h2database:h2:1.4.197",
-        "mysql"                      : "mysql:mysql-connector-java:8.0.15",
+        "mysql"                      : "mysql:mysql-connector-java:8.0.18",
         "sqlite"                     : "org.xerial:sqlite-jdbc:3.27.2.1",
         //code generator
         "velocity"                   : "org.apache.velocity:velocity-engine-core:2.1",