Make compiletime.testing.Error final

Co-Authored-By: Jamie Thompson <[email protected]>

Author: anatoliykmetyuk

library/src/scala/compiletime/testing/Error.scala

@@ -9,7 +9,7 @@ package scala.compiletime.testing
  *  version to version. This API is to be used for testing purposes
  *  only.
  */
-case class Error(message: String, lineContent: String, column: Int, kind: ErrorKind)
+final case class Error(message: String, lineContent: String, column: Int, kind: ErrorKind)
 
 /** An error can be either a parse-time or a typecheck-time */
 sealed trait ErrorKind  // TODO make this enum, so far not doable because ScalaJS compilation fails on it