Remove env setting side effect.

Env variables 'AWS_ACCESS_KEY_ID' and 'AWS_SECRET_ACCESS_KEY' are no longer set if they are not present in env. Before credentials were passed explicitely, this was necessary for authentication since there was no other mechanism implemented than to set the env variables.

minimalkv/net/s3fsstore.py

@@ -184,13 +184,11 @@ def _from_parsed_url(
 
         if url_access_key_id is None:
             url_secret_access_key = os.environ.get("AWS_ACCESS_KEY_ID")
-        else:
-            os.environ["AWS_ACCESS_KEY_ID"] = url_access_key_id
+            # TODO: Should we allow these attributes to be none-able?
+            # A potential use case might be a public bucket
 
         if url_secret_access_key is None:
             url_secret_access_key = os.environ.get("AWS_SECRET_ACCESS_KEY")
-        else:
-            os.environ["AWS_SECRET_ACCESS_KEY"] = url_secret_access_key
 
         credentials = Credentials(
             access_key_id=url_access_key_id,