Update plugin com.diffplug.spotless to v7 (#329)

| datasource | package                                                   | from   | to    |
| ---------- | --------------------------------------------------------- | ------ | ----- |
| maven      | com.diffplug.spotless:com.diffplug.spotless.gradle.plugin | 6.25.0 | 7.0.0 |

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

build.gradle.kts

@@ -13,7 +13,7 @@ import java.net.URL
 
 plugins {
   kotlin("multiplatform") version "2.1.0"
-  id("com.diffplug.spotless") version "6.25.0"
+  id("com.diffplug.spotless") version "7.0.0"
   id("maven-publish")
   id("com.vanniktech.maven.publish") version "0.30.0"
   id("org.jetbrains.kotlinx.binary-compatibility-validator") version "0.17.0"