Addresses assumption about the directory structure

The code appears to assume a certain directory structure, where only files (not another directory) will be found.
Suggesting adding a check so that only files will be retrieved.
I would do this function differently, but here is a minimal edit to keep the code as-is as much as possible.
Let me know if you'd prefer a larger suggestion on editing.

src/populate.py

@@ -39,7 +39,7 @@ def get_evaluation_queue_df(save_path: str, cols: list) -> list[pd.DataFrame]:
             all_evals.append(data)
         elif ".md" not in entry:
             # this is a folder
-            sub_entries = [e for e in os.listdir(f"{save_path}/{entry}") if not e.startswith(".")]
+            sub_entries = [e for e in os.listdir(f"{save_path}/{entry}") if isfile(e) and not e.startswith(".")]
             for sub_entry in sub_entries:
                 file_path = os.path.join(save_path, entry, sub_entry)
                 with open(file_path) as fp: