Fix: Use FileNotFoundError for file not found in main.py

Replaced IOError with FileNotFoundError on line 320 of main.py to use a more specific and appropriate exception for file not found errors.

Author: creepereye1204

src/dotenv/main.py

@@ -200,6 +200,7 @@ def set_key(
 def unset_key(
     dotenv_path: StrPath,
     key_to_unset: str,
+    quote_mode: str = "always",
     encoding: Optional[str] = "utf-8",
 ) -> Tuple[Optional[bool], str]:
     """