Bump mysql-connector-java in /frameworks/Java/ninja-standalone

Bumps [mysql-connector-java](https://github.com/mysql/mysql-connector-j) from 8.0.18 to 8.0.28.
- [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@8.0.18...8.0.28)

---
updated-dependencies:
- dependency-name: mysql:mysql-connector-java
  dependency-type: direct:production
...

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

Author: dependabot[bot]

frameworks/Java/ninja-standalone/pom.xml

@@ -23,7 +23,7 @@
         <hibernate-validator.version>6.0.20.Final</hibernate-validator.version>
         <jaxb-api.version>2.3.0</jaxb-api.version>
         <jetty.version>9.4.18.v20190429</jetty.version>
-        <mysql.version>8.0.18</mysql.version>
+        <mysql.version>8.0.28</mysql.version>
         <ninja.version>6.5.0</ninja.version>
         <xml-apis.version>2.0.2</xml-apis.version>
     </properties>