Fix linter issues and unittests

telegram_downloader_bot/utils.py

@@ -1,5 +1,5 @@
 import os
-import pickle
+import pickle  # nosec
 import re
 
 from datetime import datetime
@@ -102,7 +102,7 @@ def get_tt_hashes() -> set:
         return set()
 
     with open(settings.tt_hash_file, "rb+") as f:
-        all_tt_hashes: set = pickle.load(f)
+        all_tt_hashes: set = pickle.load(f)  # nosec
     print(all_tt_hashes)
     return all_tt_hashes