Build: Bump com.diffplug.spotless:spotless-plugin-gradle

Bumps [com.diffplug.spotless:spotless-plugin-gradle](https://github.com/diffplug/spotless) from 6.13.0 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@plugin-gradle/6.13.0...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]>

Author: dependabot[bot]

build.gradle

@@ -28,7 +28,7 @@ buildscript {
   dependencies {
     classpath 'gradle.plugin.com.github.jengelman.gradle.plugins:shadow:7.0.0'
     classpath 'com.palantir.baseline:gradle-baseline-java:4.42.0'
-    classpath 'com.diffplug.spotless:spotless-plugin-gradle:6.13.0'
+    classpath 'com.diffplug.spotless:spotless-plugin-gradle:6.18.0'
     classpath 'gradle.plugin.org.inferred:gradle-processors:3.7.0'
     classpath 'me.champeau.jmh:jmh-gradle-plugin:0.6.8'
     classpath 'gradle.plugin.io.morethan.jmhreport:gradle-jmh-report:0.9.0'