Bump bom-2.222.x from 20 to 21

Bumps [bom-2.222.x](https://github.com/jenkinsci/pom) from 20 to 21.
- [Release notes](https://github.com/jenkinsci/pom/releases)
- [Changelog](https://github.com/jenkinsci/pom/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jenkinsci/pom/commits)

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

pom.xml

@@ -111,7 +111,7 @@
             <dependency>
                 <groupId>io.jenkins.tools.bom</groupId>
                 <artifactId>bom-2.222.x</artifactId>
-                <version>20</version>
+                <version>21</version>
                 <scope>import</scope>
                 <type>pom</type>
             </dependency>