Revert "Update plugin spotless to v7"

This reverts commit 7664e38.

gradle/libs.versions.toml

@@ -98,5 +98,5 @@ jmh = { id = "me.champeau.jmh", version = "0.7.2" }
 nexusPublish = { id = "io.github.gradle-nexus.publish-plugin", version = "2.0.0" }
 plantuml = { id = "io.freefair.plantuml", version = "8.11" }
 shadow = { id = "com.gradleup.shadow", version = "8.3.5" }
-spotless = { id = "com.diffplug.spotless", version = "7.0.0" }
+spotless = { id = "com.diffplug.spotless", version = "6.25.0" }
 versions = { id = "com.github.ben-manes.versions", version = "0.51.0" }