sdss/marvin: Marvin Beta 2.8.0

This release pins the minimum Python version to >=3.8, and drops support for all Python versions 5, Jinja2>3, markupsafe>2.1. What's Changed Relax deps and bump min python to >3.8 by @havok2063 in https://github.com/sdss/marvin/pull/783 Updating Flask package dependencies by @havok2063 in https://github.com/sdss/marvin/pull/784 Bump rtd python version by @havok2063 in https://github.com/sdss/marvin/pull/785 updating rtd config yaml by @havok2063 in https://github.com/sdss/marvin/pull/786 Updates test suite by @havok2063 in https://github.com/sdss/marvin/pull/787 Updating api code for deprecation warnings by @havok2063 in https://github.com/sdss/marvin/pull/788 Full Changelog: https://github.com/sdss/marvin/compare/2.7.4...2.8.