Upgrade hub envs pip from 21.3.* to 23.1.*

[consideRatio]

The hub env's pip is upgraded as part of running the bootstrap script here:

https://github.com/jupyterhub/the-littlest-jupyterhub/blob/3e2f8cabfd8743929bb90f735d24b91f8386b29e/bootstrap/bootstrap.py#L478-L482

Here is info about changes since 21.3: https://pip.pypa.io/en/stable/news/