Bump mysql-connector-java from 5.1.40 to 8.0.16 in /back-end (#150)

Bumps [mysql-connector-java](https://github.com/mysql/mysql-connector-j) from 5.1.40 to 8.0.16.
- [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@5.1.40...8.0.16)

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

back-end/pom.xml

@@ -38,7 +38,7 @@
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
-            <version>5.1.40</version>
+            <version>8.0.16</version>
         </dependency>
 
         <dependency>