More readable YAML syntax

[paddyroddy]

Suggestion to split up #207. To be merged after #210, #212.

[samcunliffe]

🤷 Meh.

I'm fine with this, but I actually find the single-line list more readable.

[dstansby]

Yeah, I also find the single line (before) more readable

[dstansby]

So unless there are others with a strong preference for this PR, I'd suggest we don't merge?

[paddyroddy]

Think beyond the one line case.

In this example I find this a lot more readable than the alternative of ["--exclude", ".github", "--warn-list", "yaml[indentation]" - bearing in mind that each of these can be a list. I want to use this format as I believe it's more extendable, and the = make it really obvious that arg2 is tied to arg1
https://github.com/UCL-MIRSG/.github/blob/de59482693728701ceb43ad8f8f9ca4b03c26bc2/precommit/mirsg-hooks.yaml#L32-L38