Consider CRLF input as formatted when in check mode

[tfausak]

Although I want to encourage others to use cabal-gild-setup-action, in this repo I should be testing against the actual cabal-gild executable that was just built. Doing so will make it possible for me to change the output format and still have the tests pass, for example.

I expect this to fail initially because --mode check doesn't quite work on Windows. The problem is that the input file has CRLF line endings but the output file has LF line endings. I was aware of this before (see 3023fc096154885300542c86f000cec9fc12efcb) but chose to ignore it until now.

[tfausak]

I'm not sure how to proceed here. I have several options:

• When using --mode check, succeed if the input is formatted modulo line endings. This feels like the most user friendly, but also kind of weird to say "yeah it's formatted" when the output would actually change.
• When on Windows, emit CRLF rather than LF line endings. This feels like doing what the platform expects, but I think canonically Cabal files should use LF line endings (although I don't think this is specified).
• Add an option, like --crlf, for controlling this behavior. This feels like passing the buck, and would be annoying for most Windows users.
• Change the test suite itself to force the input file to have LF line endings. I think Git is automatically converting LF to CRLF on checkout, which is the source of this problem.