Bump mysql-connector-java from 8.0.20 to 8.0.21 in /modules/jdbc-test (#3044)

Bumps [mysql-connector-java](https://github.com/mysql/mysql-connector-j) from 8.0.20 to 8.0.21.
- [Release notes](https://github.com/mysql/mysql-connector-j/releases)
- [Changelog](https://github.com/mysql/mysql-connector-j/blob/release/8.0/CHANGES)
- [Commits](mysql/mysql-connector-j@8.0.20...8.0.21)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Richard North <[email protected]>

Author: dependabot[bot]

modules/jdbc-test/build.gradle

@@ -17,5 +17,5 @@ dependencies {
     compile 'commons-dbutils:commons-dbutils:1.7'
     compile 'org.apache.tomcat:tomcat-jdbc:9.0.37'
     compile 'org.vibur:vibur-dbcp:25.0'
-    compile 'mysql:mysql-connector-java:8.0.20'
+    compile 'mysql:mysql-connector-java:8.0.21'
 }