Bump mariadb-java-client from 2.6.0 to 2.6.1 in /modules/mariadb (#2950)

Bumps [mariadb-java-client](https://github.com/mariadb-corporation/mariadb-connector-j) from 2.6.0 to 2.6.1.
- [Release notes](https://github.com/mariadb-corporation/mariadb-connector-j/releases)
- [Changelog](https://github.com/mariadb-corporation/mariadb-connector-j/blob/master/CHANGELOG.md)
- [Commits](mariadb-corporation/mariadb-connector-j@2.6.0...2.6.1)

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

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

Author: dependabot[bot]

modules/mariadb/build.gradle

@@ -10,7 +10,7 @@ dependencies {
     compileOnly 'org.mariadb:r2dbc-mariadb:0.8.2-alpha2'
 
     testCompile project(':jdbc-test')
-    testCompile 'org.mariadb.jdbc:mariadb-java-client:2.6.0'
+    testCompile 'org.mariadb.jdbc:mariadb-java-client:2.6.1'
 
     testCompile testFixtures(project(':r2dbc'))
     testCompile 'org.mariadb:r2dbc-mariadb:0.8.1-alpha1'