fix: chained_assignment could be warn, raise or None (#779)

https://github.com/pandas-dev/pandas/blob/1.5.x/pandas/core/config_init.py#L563-L575

Author: leviplj

pandas-stubs/_config/config.pyi

@@ -118,7 +118,7 @@ class IO(DictWrapper):
     sql: IOSQL
 
 class Mode(DictWrapper):
-    chained_assignment: str
+    chained_assignment: Literal["warn", "raise"] | None
     data_manager: str
     sim_interactive: bool
     string_storage: str

pandas-stubs/core/config_init.pyi

@@ -1,3 +1,5 @@
+from typing import Literal
+
 use_bottleneck_doc: str = ...
 
 def use_bottleneck_cb(key) -> None: ...
@@ -49,7 +51,7 @@ use_inf_as_na_doc: str = ...
 
 def use_inf_as_na_cb(key) -> None: ...
 
-chained_assignment: str = ...
+chained_assignment: Literal["warn", "raise"] | None
 reader_engine_doc: str = ...
 writer_engine_doc: str = ...
 parquet_engine_doc: str = ...