tests: fixed assertion checking error content

Verifiable consumer may fail with two different messages when consuming
while the topic is being deleted. Accounting for all the messages in the
assertion checking error reporting.

Fixes: #11306

Signed-off-by: Michal Maslanka <michal@redpanda.com>

tests/rptest/tests/simple_e2e_test.py

@@ -67,4 +67,5 @@ def test_consumer_interruption(self):
             error = e
 
         assert error is not None
-        assert "Consumed from an unexpected" in str(error)
+        assert "Consumed from an unexpected" in str(
+            error) or "is behind the current committed offset" in str(error)