Bump spotless-maven-plugin from 2.20.0 to 2.21.0

Bumps [spotless-maven-plugin](https://github.com/diffplug/spotless) from 2.20.0 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/2.20.0...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] <[email protected]>

Author: dependabot[bot]

pom.xml

@@ -161,7 +161,7 @@
       <plugin>
         <groupId>com.diffplug.spotless</groupId>
         <artifactId>spotless-maven-plugin</artifactId>
-        <version>2.20.0</version>
+        <version>2.21.0</version>
         <executions>
           <execution>
             <goals>