fix:mypy type errors resolved

Author: invain01

pandas/_testing/_io.py

@@ -61,13 +61,18 @@ def round_trip_pickle(
         # Only join tmpdir with _path when _path is a string or Path-like.
         # _path may be a ReadPickleBuffer (file-like) in which case it
         # should be used directly for pickle operations.
-        temp_path: pathlib.Path | ReadPickleBuffer
         if isinstance(_path, (str, pathlib.Path)):
-            temp_path = pathlib.Path(tmpdir) / _path
+            temp_path: FilePath = pathlib.Path(tmpdir) / _path
+            pd.to_pickle(obj, temp_path)
         else:
-            temp_path = _path
-        pd.to_pickle(obj, temp_path)
-        return pd.read_pickle(temp_path)
+            # _path is a ReadPickleBuffer (file-like object)
+            pd.to_pickle(obj, _path)  # type: ignore[arg-type]
+
+        # For read_pickle, handle both cases
+        if isinstance(_path, (str, pathlib.Path)):
+            return pd.read_pickle(pathlib.Path(tmpdir) / _path)
+        else:
+            return pd.read_pickle(_path)
 
 
 def round_trip_pathlib(writer, reader, path: str | None = None):