GitHub integration unable to fetch issues

[sentry]

Sentry Issue: FLAGSMITH-API-5K9

TypeError: Issuer (iss) must be a string.
(19 additional frame(s) were not displayed)
...
  File "integrations/github/views.py", line 85, in wrapper
    return func(*args, **kwargs)  # type: ignore[no-any-return]
  File "integrations/github/views.py", line 230, in fetch_issues
    data = fetch_search_github_resource(
  File "integrations/github/client.py", line 187, in fetch_search_github_resource
    headers: dict[str, str] = build_request_headers(
  File "integrations/github/client.py", line 40, in build_request_headers
    else generate_token(
  File "integrations/github/client.py", line 62, in generate_token
    token = auth.token