Bump minimum version of httpx to 0.24

[chrisinmtown]

Make tests work in Python 3.13 by avoiding httpx version 0.23 import of package cgi

Changes proposed in this pull request:

• Change pyproject.toml to require httpx at minimum version 0.24, which does not use cgi

[chrisinmtown]

When I run the tox suite from the beginning, in the py39-min run, poetry pins the httpx version at the minimum version 0.23.0. The poetry.lock fie persists across the following tox runs. This fails when it reaches py3.13 because package httpx==0.23.0 imports package cgi which is not available in py3.13.

If I change the tox.ini command to be poetry lock--regenerate then all tests pass including python 3.13. In fact, with that new option in place, I don't have to bump the minimum version of httpx.

Please comment. I'll be glad to change this PR to leave the versions alone and just change tox.ini

[coveralls]

coverage: 94.297%. remained the same
when pulling 983353a on chrisinmtown:upgr-httpx-min-ver
into df9960b on spec-first:main.

[chrisinmtown]

I still recommend this version bump, but this PR is largely superseded by #2098