fix(deps): bump com.diffplug.spotless from 5.14.2 to 6.20.0

Bumps com.diffplug.spotless from 5.14.2 to 6.20.0.

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

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -11,7 +11,7 @@ plugins {
     id("org.jetbrains.kotlin.jvm") version "$kotlinVersion"
     id('java-library')
     id("org.jetbrains.dokka") version "1.8.20"
-    id("com.diffplug.spotless") version "5.14.2"
+    id("com.diffplug.spotless") version "6.20.0"
     id('jacoco')
     id('idea')