ci: add github ci intergration to ensure PRs build successfully

[acuteaangle]

This adds GitHub Actions integration to automatically build (and run tests, should they be added in the future) on Windows, MacOS, and Linux.

This will (hopefully) prevent issues like gh-87 (introduced by gh-83) from recurring in the future.

Related-to: gh-83, gh-86, gh-87

[prochac]

Does it pass if it's run on top of https://github.com/Spagett1/pineflash/pull/86 ? Then it should, right?

[acuteaangle]

It does, here are the logs and results.

[acuteaangle]

force-pushed to resolve trailing whitespace and correct linux job name to test.

1:  0989ea8fc4ac ! 1:  cd95a0db0afb ci: add github ci intergration to ensure PRs build successfully
@@ .github/workflows/tests.yaml (new)
 +  - push
 +  - pull_request
 +
-+env: 
++env:
 +  CARGO_TERM_COLOR: always
 +
 +jobs:
-+  linux:
++  test:
 +    name: Build and Test
 +    runs-on: ${{ matrix.os }}
 +    strategy: