Bump minimum PHP version from 7.4 to 8.0

[dkotter]

Description of the Change

This PR bumps the minimum supported PHP version from 7.4 to 8.0. This PR is an alternative to #177, so see that issue for full details on what this solves.

Changelog Entry

Changed - Bump minimum PHP version from 7.4 to 8.0

Credits

Props @dkotter

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests pass.