Add GitHub workflow for CI

[kwridan]

Describe your changes

• A new xcdiff GitHub workflow is being added for CI
• Currently configures 2 separate jobs
  • Linting
  • Build & Test
• The build and test were grouped together as running them on the same node allows re-using some of the cached build artefacts

Additional context

We'd like to migrate off of Travis to GitHub Actions, this PR introduces the GitHub workflow, once verified we can remove the .travis.yml file.

[codecov]

Codecov Report

Merging #93 (b9dc537) into main (f898d30) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #93   +/-   ##
=======================================
  Coverage   96.22%   96.22%           
=======================================
  Files          47       47           
  Lines        1853     1853           
=======================================
  Hits         1783     1783           
  Misses         70       70           

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[kwridan]

Pushed a few updates to include:

• Specifying GitHub token permissions (made it a bit more restricted)
• Added caching support to speed up builds

Some example runs from my fork:

On a PR:
kwridan#1

On main:
https://github.com/kwridan/xcdiff/actions

The bit that I'm not a 100% sure on is CodeCov integration, we may need to add a GitHub secret to pass along its token. That may cause some friction on PRs from forks as secrets may not be available in that scenario 🤔

There's also a dedicated CodeCov action we may be able to leverage https://github.com/codecov/codecov-action

[kwridan]

I've ran another test with CodeCov enabled on my personal fork - I didn't need to setup a token for it either (seems to not be required for public repos)

kwridan#2

[marciniwanicki]

👍

[kwridan]

As a final test - here's an example verifying fork PRs workflows

kwridan#3