Bump spotless-maven-plugin from 2.20.2 to 2.21.0

Bumps [spotless-maven-plugin](https://github.com/diffplug/spotless) from 2.20.2 to 2.21.0.
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](diffplug/spotless@lib/2.20.2...lib/2.21.0)

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pom.xml

@@ -89,7 +89,7 @@
     <buildnumber.plugin.version>1.4</buildnumber.plugin.version>
     <jruby.version>9.3.3.0</jruby.version>
     <jmh.version>1.34</jmh.version>
-    <spotless.version>2.20.2</spotless.version>
+    <spotless.version>2.21.0</spotless.version>
     <jacoco.version>0.8.7</jacoco.version>
     <!-- to sign artifacts when releasing -->
     <gpg.keyname>6026DFCA</gpg.keyname>