Bump mysql-connector-java from 8.0.16 to 8.0.28 in /spring-boot/sjdemo

Bumps [mysql-connector-java](https://github.com/mysql/mysql-connector-j) from 8.0.16 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](https://github.com/mysql/mysql-connector-j/compare/8.0.16...8.0.28)

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

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

spring-boot/sjdemo/pom.xml

@@ -39,7 +39,7 @@
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
-            <version>8.0.16</version>
+            <version>8.0.28</version>
         </dependency>
         <dependency>
             <groupId>io.shardingsphere</groupId>