[bot]: bump org.codehaus.mojo:versions-maven-plugin

Bumps [org.codehaus.mojo:versions-maven-plugin](https://github.com/mojohaus/versions) from 2.15.0 to 2.21.0.
- [Release notes](https://github.com/mojohaus/versions/releases)
- [Changelog](https://github.com/mojohaus/versions/blob/master/ReleaseNotes.md)
- [Commits](mojohaus/versions@2.15.0...2.21.0)

---
updated-dependencies:
- dependency-name: org.codehaus.mojo:versions-maven-plugin
  dependency-version: 2.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

build/optaplanner-build-parent/pom.xml

@@ -83,7 +83,7 @@
     <version.revapi.plugin>0.15.0</version.revapi.plugin>
     <version.sniffer.plugin>1.23</version.sniffer.plugin>
     <version.surefire.plugin>3.0.0</version.surefire.plugin>
-    <version.versions.plugin>2.15.0</version.versions.plugin>
+    <version.versions.plugin>2.21.0</version.versions.plugin>
 
     <!-- Plugin configuration properties -->
     <maven.min.version>3.8.1</maven.min.version>