Don't touch files if they don't need changing

[piegamesde]

Fixes #88

This has not been tested yet, CC @SebTM please take a look

[SebTM]

Thanks very much for looking into this as fast as you did 🚀
Works well, tested it as following:

Modified mtime of flake.nix via touch -mt 0911171533 flake.nix and ran new build of nixfmt:

-rw-r--r-- 1 sebtm users  3330 Nov 17  2009 flake.nix
dist-newstyle/build/x86_64-linux/ghc-9.0.2/nixfmt-0.5.0/x/nixfmt/build/nixfmt/nixfmt flake.nix
-rw-r--r-- 1 sebtm users  3330 Nov 17  2009 flake.nix

running afterwards my old install of nixfmt results in:

-rw-r--r-- 1 sebtm users  3330 Nov 17  2009 flake.nix
nixfmt flake.nix
-rw-r--r-- 1 sebtm users  3330 Sep 26 02:15 flake.nix

which demonstrates the difference again :) so LGTM

[infinisil]

I'd merge, but can't because CI doesn't seem to run

[piegamesde]

CI doesn't seem to be running, I have no idea what's happening there. I could probably manually merge and push to master, but that would be undesirable. The CI is broken in #132 too btw

[Lucus16]

We'll need to get #134 merged for CI to work. If you don't want to wait for it, just run CI locally and then merge to master manually.