Update httpx dependency to allow `0.24.1`

[travis-cook-sfdc]

0.24 was released a two months ago and includes a ton of additional logging improvements. I'd love to turn these on, but I can't because pinotdb restricts to >=0.23.0,<0.24.0.

Generally, I don't think using ^ is a good idea in any package, it's much better to use >= because then it leaves the responsibility to the client to find breaking changes when upgrading and resolving them or forcing a lower version. Library developers shouldn't be responsible for this.

https://hynek.me/articles/semver-will-not-save-you/