Add spotless formatter step to revert copyright year only changes (#1518)

This avoids an issue where, during the course of development, a file is
touched, thus modifying the copyright year.
Then, undoing the previous change does not undo the copyright year
change.

buildSrc/src/main/kotlin/pklJavaLibrary.gradle.kts

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,12 +50,17 @@ artifacts {
 }
 
 spotless {
+  val revertYearOnlyChanges = RevertYearOnlyChangesStep(rootProject.rootDir, ratchetFrom!!).create()
+
   java {
+    addStep(revertYearOnlyChanges)
     googleJavaFormat(libs.versions.googleJavaFormat.get())
     target("src/*/java/**/*.java")
     licenseHeaderFile(rootProject.file("buildSrc/src/main/resources/license-header.star-block.txt"))
   }
+
   kotlin {
+    addStep(revertYearOnlyChanges)
     ktfmt(libs.versions.ktfmt.get()).googleStyle()
     target("src/*/kotlin/**/*.kt")
     licenseHeaderFile(rootProject.file("buildSrc/src/main/resources/license-header.star-block.txt"))