Failure in SchemaRegistryTest.test_mode

[NyaliaLui]

https://buildkite.com/redpanda/redpanda/builds/13260#0182451f-df0f-433f-a0d9-7317a209c0d2/6-8557

[dotnwat]

@NyaliaLui please add a little context so that it's easier to determine when its the same test but a different failure mode.

test_id:    rptest.tests.schema_registry_test.SchemaRegistryTest.test_mode
--
  | status:     FAIL
  | run time:   10.984 seconds
  |  
  |  
  | KeyError('mode')
  | Traceback (most recent call last):
  | File "/usr/local/lib/python3.10/dist-packages/ducktape/tests/runner_client.py", line 135, in run
  | data = self.run_test()
  | File "/usr/local/lib/python3.10/dist-packages/ducktape/tests/runner_client.py", line 227, in run_test
  | return self.test_context.function(self.test)
  | File "/root/tests/rptest/services/cluster.py", line 35, in wrapped
  | r = f(self, *args, **kwargs)
  | File "/root/tests/rptest/tests/schema_registry_test.py", line 635, in test_mode
  | assert result_raw.json()["mode"] == "READWRITE"
  | KeyError: 'mode'

[dotnwat]

@BenPope weird

[BenPope]

Duplicate of #5725