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

@@ -37,7 +37,7 @@ buildscript {
     // So, bump checkstyle to the latest java 8 supported version(9.3) which contains the fix.
     classpath "com.puppycrawl.tools:checkstyle:9.3"
 
-    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:0.7.0'
     classpath 'gradle.plugin.io.morethan.jmhreport:gradle-jmh-report:0.9.0'