Investigate ways to perform the commit linting action without requiring "fetch-depth: 0" at checkout

[iainjreid]

The checkout action only pulls down a single commit to maximise performance, and whilst this is a great feature, it creates some problems for our commit linting action (the solution being to checkout the entire history by passing fetch-depth: 0 to the checkout action).

We should find a way to still achieve the commit linting, without requiring the developer to pull down their entire project history.