fix: tmp directory

app.py

@@ -32,12 +32,12 @@ transformer_vectorizer = TransformerVectorizer()
 def clean_tmp_directory():
     # Allow 20 user keys to be stored.
     # Once that limitation is reached, deleted the oldest.
-    list_files = sorted(Path(".fhe_keys/").iterdir(), key=os.path.getmtime)
+    path_sub_directories = sorted([f for f in Path(".fhe_keys/").iterdir() if f.is_dir()], key=os.path.getmtime)
 
     user_ids = []
-    if len(list_files) > N_USER_KEY_STORED:
-        n_files_to_delete = len(list_files) - N_USER_KEY_STORED
-        for p in list_files[:n_files_to_delete]:
+    if len(path_sub_directories) > N_USER_KEY_STORED:
+        n_files_to_delete = len(path_sub_directories) - N_USER_KEY_STORED
+        for p in path_sub_directories[:n_files_to_delete]:
             user_ids.append(p.name)
             shutil.rmtree(p)