Increase deprecation level of Job.cancel(cause) to ERROR

Author: elizarov

kotlinx-coroutines-core/common/src/Job.kt

@@ -169,10 +169,13 @@ public interface Job : CoroutineContext.Element {
     public fun cancel(): Unit
 
     /**
-     * @suppress
+     * @suppress **Deprecated**: This function is obsolete.
+     *   Use [CompletableJob.completeExceptionally] or [CompletableDeferred.completeExceptionally] with exception,
+     *   or [Job.cancel] without exception instead.
      */
     @ObsoleteCoroutinesApi
-    @Deprecated(level = DeprecationLevel.WARNING, message = "Use CompletableDeferred.completeExceptionally(cause) or Job.cancel() instead",
+    @Deprecated(level = DeprecationLevel.ERROR,
+        message = "Use completeExceptionally(cause) on CompletableDeferred/Job or Job.cancel() without exception instead",
         replaceWith = ReplaceWith("cancel()")
     )
     public fun cancel(cause: Throwable? = null): Boolean