Bump com.diffplug.spotless:spotless-plugin-gradle from 6.17.0 to 6.18.0

Bumps [com.diffplug.spotless:spotless-plugin-gradle](https://github.com/diffplug/spotless) from 6.17.0 to 6.18.0.
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](diffplug/spotless@gradle/6.17.0...gradle/6.18.0)

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

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

buildSrc/build.gradle.kts

@@ -4,5 +4,5 @@ repositories { gradlePluginPortal() }
 
 dependencies {
   implementation("info.solidsoft.gradle.pitest:gradle-pitest-plugin:1.9.11")
-  implementation("com.diffplug.spotless:spotless-plugin-gradle:6.17.0")
+  implementation("com.diffplug.spotless:spotless-plugin-gradle:6.18.0")
 }