No longer restrict `pandas` to be version 1.X. Also, remove explicit support and CI testing for python 3.7, and add CI testing for 3.12.
Normally, due to the loss of functionality for 3.7, we'd call this `v3.0`, however that is reserved for the new version of the front end.
There should be no functional changes.
What's Changed
* Remove pandas restrictions by gordonwatts in https://github.com/ssl-hep/ServiceX_frontend/pull/358
**Full Changelog**: https://github.com/ssl-hep/ServiceX_frontend/compare/v2.7.2...v2.8.0