Merge pull request #4 from SFuller4/to-json-append-mode

updating typing issues in the core file

Author: SFuller4

pandas/core/generic.py

@@ -2400,7 +2400,7 @@ def to_json(
         index: bool_t = True,
         indent: int | None = None,
         storage_options: StorageOptions = None,
-        mode: str = "w",
+        mode: Literal["a", "w"] = "w",
     ) -> str | None:
         """
         Convert the object to a JSON string.