Bump com.diffplug.spotless from 6.3.0 to 6.4.0 (#569)

Author: dependabot[bot]

build.gradle

@@ -4,7 +4,7 @@ plugins {
 	id 'maven-publish'
 	id 'signing'
 	id 'pmd' // code check, working on source code
-	id 'com.diffplug.spotless' version '6.3.0'//code format
+	id 'com.diffplug.spotless' version '6.4.0'//code format
 	id 'com.github.spotbugs' version '5.0.6' // code check, working on byte code
 	id 'de.undercouch.download' version '5.0.2'
 	id 'kr.motd.sphinx' version '2.10.1' // documentation generation