Update plugin spotless to v8.4.0

Author: renovate[bot]

gradle/libs.versions.toml

@@ -71,7 +71,7 @@ kotlin-multiplatform = { id = "org.jetbrains.kotlin.multiplatform", version.ref
 kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
 kover = { id = "org.jetbrains.kotlinx.kover", version.ref = "kover" }
 shadow = "com.gradleup.shadow:9.4.1"
-spotless = "com.diffplug.spotless:8.3.0"
+spotless = "com.diffplug.spotless:8.4.0"
 
 # Project conventional plugins
 valkyrie-jvm = { id = "valkyrie.jvm" }