ducktape: disable test_replica_placement.num_partitions=400

...in debug mode. Runs are failing with timeout in topic creation.

Creation doesn't return control until all partitions are assigned
leaders. Raft groups are created but the RPCs to other nodes are repeatedly
timing out resulting in leaderlessness. Disabling the test until we
get to the bottom of it.

tests/rptest/tests/rack_aware_replica_placement_test.py

@@ -9,16 +9,16 @@
 
 import random
 import os
+from collections import defaultdict
 from ducktape.utils.util import wait_until
 from ducktape.mark import matrix
 from rptest.clients.types import TopicSpec
 from rptest.clients.rpk import RpkTool
 from rptest.services.admin import Admin
-
 from rptest.clients.default import DefaultClient
 from rptest.services.cluster import cluster
 from rptest.tests.redpanda_test import RedpandaTest
-from collections import defaultdict
+from rptest.utils.mode_checks import cleanup_on_early_exit
 
 
 class RackAwarePlacementTest(RedpandaTest):
@@ -114,6 +114,14 @@ def test_replica_placement(self, rack_layout_str, num_partitions,
         @param replication_factor defines recplication factor of all partitions.
         """
 
+        # https://github.com/redpanda-data/redpanda/issues/11276
+        if self.debug_mode and num_partitions == 400:
+            self.logger.info(
+                "Disabling test in debug mode due to slowness/timeouts with large number of partitions."
+            )
+            cleanup_on_early_exit(self)
+            return
+
         rack_layout = [str(i) for i in rack_layout_str]
         assert len(rack_layout) == 6