Fix greenlet dependency in poetry lock file. (#712)

* Fix `greenlet` dependency in poetry lock file.

It looks like poetry on macOS does not install `greenlet`, while it
does on Linux, both for version 1.8.4 and 2.0.1, which seems to be a
bug. Additionally, failures only manifest after _using_ codegate, and
not during startup.

This change adds `greenlet` package to `pyproject.toml`.

Co-authored-by: Luke Hinds <luke@stacklok.com>

Author: blkt