[MINOR][PYTHON][ML][TESTS] Further skip flaky test_parity_regression

### What changes were proposed in this pull request?
Further skip flaky `test_parity_regression`

### Why are the changes needed?
it gets stuck sometimes

https://github.com/apache/spark/actions/runs/16204789449/job/45752455040

skip it for now

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
CI

### Was this patch authored or co-authored using generative AI tooling?
no

Closes #51448 from zhengruifeng/further_skip_regression.

Authored-by: Ruifeng Zheng <[email protected]>
Signed-off-by: Ruifeng Zheng <[email protected]>

Author: zhengruifeng

python/pyspark/ml/tests/connect/test_parity_classification.py

@@ -21,6 +21,7 @@
 from pyspark.testing.connectutils import ReusedConnectTestCase
 
 
+# TODO(SPARK-52764): Re-enable this test after fixing the flakiness.
 @unittest.skip("Disabled due to flakiness, should be enabled after fixing the issue")
 class ClassificationParityTests(ClassificationTestsMixin, ReusedConnectTestCase):
     pass

python/pyspark/ml/tests/connect/test_parity_clustering.py

@@ -21,6 +21,7 @@
 from pyspark.testing.connectutils import ReusedConnectTestCase
 
 
+# TODO(SPARK-52764): Re-enable this test after fixing the flakiness.
 @unittest.skip("Disabled due to flakiness, should be enabled after fixing the issue")
 class ClusteringParityTests(ClusteringTestsMixin, ReusedConnectTestCase):
     pass

python/pyspark/ml/tests/connect/test_parity_regression.py

@@ -21,6 +21,8 @@
 from pyspark.testing.connectutils import ReusedConnectTestCase
 
 
+# TODO(SPARK-52764): Re-enable this test after fixing the flakiness.
+@unittest.skip("Disabled due to flakiness, should be enabled after fixing the issue")
 class RegressionParityTests(RegressionTestsMixin, ReusedConnectTestCase):
     pass