Update CI

[coruscating]

• Update old GitHub Actions and add dependabot for automatic Github Actions updates
• Add concurrency check to stop old CI jobs if there are new pushes to the PR
• Add macos and windows tests
• Add caching during tests
• Prevent CI from running automatically on forks

[coruscating]

@drewvandeth Since the tests have been replaced with new OS-dependent ones, you'll have to update the required checks in the settings to remove the old tests and replace them with the new ones.