Bump com.diffplug.spotless:spotless-plugin-gradle from 8.2.1 to 8.4.0

Bumps [com.diffplug.spotless:spotless-plugin-gradle](https://github.com/diffplug/spotless) from 8.2.1 to 8.4.0.
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](diffplug/spotless@gradle/8.2.1...gradle/8.4.0)

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-plugin-gradle
  dependency-version: 8.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

buildSrc/build.gradle.kts

@@ -30,7 +30,7 @@ dependencies {
   implementation(gradleApi())
 
   // When updating, update above in plugins too
-  implementation("com.diffplug.spotless:spotless-plugin-gradle:8.2.1")
+  implementation("com.diffplug.spotless:spotless-plugin-gradle:8.4.0")
   implementation("com.github.spotbugs.snom:spotbugs-gradle-plugin:6.4.8")
   implementation("com.gradleup.shadow:shadow-gradle-plugin:8.3.9")