Revamp CI

[CosmicHorrorDev]

The commits should be pretty self-explanatory, but in short this:

• Switches away from actions-rs actions since they're no longer maintained and usually spit out deprecation notices
• Bumps actions/checkout to the latest version
• Runs CI against beta to preemptively find any possible regressions or deprecation warnings
• Runs jobs on all pushes and pull requests, so that PRs get CI runs
• Schedules a monthly CI run to catch any issues with the latest stable and beta early

Let me know if you have any questions (this CI run should fail due to the single clippy lint)

[Aloso]

Thanks for your pull request! Once my review comment is addressed, this should be good to go 👍‍