Merge #6672: fix: intermittent error in feature_notification due to extra CL

21e6a4e fix: intermittent error in feature_notification due to extra CL (Konstantin Akimov)

Pull request description:

  ## Issue being fixed or feature implemented

  It can happen if the best block get CL too fast. Locally it fails 1 time out of 10 with error:

      2025-05-16T07:09:24.060000Z TestFramework (INFO): Mine single block, wait for chainlock
      2025-05-16T07:09:24.275000Z TestFramework (ERROR): Assertion failed
      Traceback (most recent call last):
        File "DASH/test/functional/test_framework/test_framework.py", line 162, in main
          self.run_test()
        File "DASH/test/functional/feature_notifications.py", line 121, in run_test
          assert_equal([tip], sorted(os.listdir(self.chainlocknotify_dir)))
        File "DASH/test/functional/test_framework/util.py", line 69, in assert_equal
          raise AssertionError("not(%s)" % " == ".join(str(arg) for arg in (thing1, thing2) + args))
      AssertionError: not(['21b88334ae6fc29ee3bb7c89dd760dad5dc8ce1064db370dc697b3da4c4315e0'] == ['21b88334ae6fc29ee3bb7c89dd760dad5dc8ce1064db370dc697b3da4c4315e0', '4fe83a613290bd755fba25da02f493376a96971b119884831a75cea33032718d'])
      2025-05-16T07:09:24.326000Z TestFramework (INFO): Stopping nodes

  ## What was done?
  We should expect CL not only for tip but for block before tip, if CL has been formed really fast.

  ## How Has This Been Tested?
  Run feature_notifications.py multiple times with these extra changes #6671

  ## Breaking Changes
  N/A

  ## Checklist:
  - [x] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone

ACKs for top commit:
  UdjinM6:
    utACK 21e6a4e
  PastaPastaPasta:
    utACK 21e6a4e

Tree-SHA512: 552ba9f25c7ef15ea7392b90f4d57577b7a9b2ab088325f7ba817d091be54e9d8b3d39129e73cff391ade5ddeb52af877575dfbc428b704931a412c619f08523

Author: PastaPastaPasta

test/functional/feature_notifications.py

@@ -115,10 +115,15 @@ def run_test(self):
 
         self.log.info("Mine single block, wait for chainlock")
         self.bump_mocktime(1)
+        pre_tip = self.nodes[0].getbestblockhash()
         tip = self.generate(self.nodes[0], 1, sync_fun=self.no_op)[-1]
         self.wait_for_chainlocked_block_all_nodes(tip)
         # directory content should equal the chainlocked block hash
-        assert_equal([tip], sorted(os.listdir(self.chainlocknotify_dir)))
+        cl_hashes = sorted(os.listdir(self.chainlocknotify_dir))
+        if len(cl_hashes) <= 1:
+            assert_equal([tip], cl_hashes)
+        else:
+            assert_equal(sorted([tip, pre_tip]), cl_hashes)
 
         if self.is_wallet_compiled():
             self.log.info("test -instantsendnotify")