build(deps): bump com.diffplug.spotless from 5.13.0 to 6.20.0

Bumps com.diffplug.spotless from 5.13.0 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

@@ -1,6 +1,6 @@
 plugins {
   id "org.sonarqube" version "3.3"
-  id "com.diffplug.spotless" version "5.13.0"
+  id "com.diffplug.spotless" version "6.20.0"
   id "org.gradle.crypto.checksum" version "1.2.0"
   id "com.github.spotbugs" version "4.7.1"
 }