Merge pull request #3 from SFuller4/to-json-append-mode

Adjusting Typing from str to Literal["a", "w"] per request.

Author: SFuller4

pandas/io/json/_json.py

@@ -136,7 +136,7 @@ def to_json(
     index: bool = True,
     indent: int = 0,
     storage_options: StorageOptions = None,
-    mode: str = "w",
+    mode: Literal["a", "w"] = "w",
 ) -> str | None:
 
     if not index and orient not in ["split", "table"]: