[TODO] Add clock drift protection in JWT generator

[webknjaz]

https://docs.github.com/en/apps/creating-github-apps/authenticating-with-a-github-app/generating-a-json-web-token-jwt-for-a-github-app#about-json-web-tokens-jwts has the following recommendation:

To protect against clock drift, we recommend that you set this 60 seconds in the past and ensure that your server's date and time is set accurately (for example, by using the Network Time Protocol).

PyGitHub implements it like this: https://github.com/PyGithub/PyGithub/blob/d90323f/github/Consts.py#L174C25-L174C28 + https://github.com/PyGithub/PyGithub/blob/d90323f/github/Auth.py#L253-L260.

And snekomatic does this: https://github.com/python-trio/snekomatic/blob/43e8e6d/snekomatic/gh.py#L86-L93 + https://github.com/python-trio/snekomatic/blob/43e8e6d/snekomatic/gh.py#L170-L179.