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

Co-authored-by: Silvan Mosberger <[email protected]>

CHANGELOG.md

@@ -11,7 +11,7 @@
 
 * Fix escaping of interpolations after dollar signs.
 * Fix nixfmt trying to allocate temp files that aren't used.
-* Fix treefmt compatibility
+* Don't write if files didn't change, fixing treefmt compatibility
 * Nixfmt now accepts the '-' argument to read from stdin.
 * `nixfmt [dir]` now recursively formats nix files in that directory.
 * Float and int literal parsing now matches nix.