Update utils.py

the function `test_raises_not_implemented_error()` in test file `test_read_df.py` on account that it was receiving a `ValueError` when it expected a `NotImplementedError`. I switched the error within `utils.py:read_df()` to be an expected `NotImplementedError`.

flepimop/gempyor_pkg/src/gempyor/utils.py

@@ -94,7 +94,7 @@ def read_df(
         )
     elif path.suffix == ".parquet":
         return pd.read_parquet(path, engine="pyarrow")
-    raise ValueError(
+    raise NotImplementedError(
         f"Invalid extension provided: '{path.suffix[1:]}'. Supported extensions are `.csv` or `.parquet`."
     )