Bump spotless-maven-plugin from 2.20.2 to 2.21.0 (#120)

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
...

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

pom.xml

@@ -183,7 +183,7 @@
             <plugin>
                 <groupId>com.diffplug.spotless</groupId>
                 <artifactId>spotless-maven-plugin</artifactId>
-                <version>2.20.2</version>
+                <version>2.21.0</version>
                 <configuration>
                     <java>
                         <prettier>