Merge pull request redpanda-data#16280 from vbotbuildovich/backport-p…

…r-16127-v23.2.x-666

[v23.2.x] rptest: Wait for the group to be in a stable state before starting tests

tests/rptest/tests/consumer_group_test.py

@@ -91,7 +91,7 @@ def create_consumers(self,
 
         def group_is_ready():
             gr = rpk.group_describe(group=group, summary=True)
-            return gr.members == consumer_count
+            return gr.members == consumer_count and gr.state == "Stable"
 
         wait_until(group_is_ready, 60, 1)
         return consumers