make CommitFailedException member fields final

Author: scottsand-db

kernel/kernel-api/src/main/java/io/delta/kernel/commit/CommitFailedException.java

@@ -31,8 +31,8 @@
  */
 public class CommitFailedException extends Exception {
 
-  public boolean retryable;
-  public boolean conflict;
+  public final boolean retryable;
+  public final boolean conflict;
 
   public CommitFailedException(boolean retryable, boolean conflict, String message) {
     super(message);