PTFE-1481 ensure private key is bytes

bert_e/git_host/github/__init__.py

@@ -53,7 +53,7 @@ def __init__(self, login: str, password: str, email: str,
         self.password = password
         self.app_id = app_id
         self.installation_id = installation_id
-        self.private_key = jwk_from_pem(private_key)
+        self.private_key = jwk_from_pem(private_key.encode('utf-8')) if private_key else None
         self.email = email
         self.org = org
         self.base_url = base_url.rstrip('/')