build(deps-dev): bump com.diffplug.spotless:spotless-maven-plugin

Bumps [com.diffplug.spotless:spotless-maven-plugin](https://github.com/diffplug/spotless) from 3.1.0 to 3.7.0.
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](diffplug/spotless@lib/3.1.0...maven/3.7.0)

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-maven-plugin
  dependency-version: 3.7.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/pom.xml

@@ -134,7 +134,7 @@
             <plugin>
                 <groupId>com.diffplug.spotless</groupId>
                 <artifactId>spotless-maven-plugin</artifactId>
-                <version>3.1.0</version>
+                <version>3.7.0</version>
                 <configuration>
                     <java>
                         <googleJavaFormat/>