return default channel buffer size for these tests (#9439)

Author: gridnevvvit

ydb/tests/functional/serializable/ya.make

@@ -1,5 +1,7 @@
 PY3TEST()
 
+ENV(YDB_CHANNEL_BUFFER_SIZE="8388608")
+
 PEERDIR(
     ydb/tests/tools/ydb_serializable/lib
     ydb/public/sdk/python

ydb/tests/library/harness/kikimr_config.py

@@ -377,6 +377,9 @@ def __init__(
         if os.getenv("YDB_HARD_MEMORY_LIMIT_BYTES"):
             self.yaml_config["memory_controller_config"] = {"hard_limit_bytes": int(os.getenv("YDB_HARD_MEMORY_LIMIT_BYTES"))}
 
+        if os.getenv("YDB_CHANNEL_BUFFER_SIZE"):
+            self.yaml_config["table_service_config"]["resource_manager"]["channel_buffer_size"] = int(os.getenv("YDB_CHANNEL_BUFFER_SIZE"))
+
         if pg_compatible_expirement:
             self.yaml_config["table_service_config"]["enable_prepared_ddl"] = True
             self.yaml_config["table_service_config"]["enable_ast_cache"] = True