treefmt: disable yamlfmt newline trimming

Signed-off-by: Paul Meyer <[email protected]>

treefmt.nix

@@ -19,7 +19,6 @@
     shellcheck.enable = true;
     shfmt.enable = true;
     statix.enable = true;
-    yamlfmt.enable = true;
     # keep-sorted end
   };
   settings.formatter = {
@@ -49,5 +48,14 @@
         "LICENSE"
       ];
     };
+    # TODO(katexochen): move back to programs after
+    # https://github.com/numtide/treefmt-nix/pull/193 is merged.
+    yamlfmt = {
+      command = "${lib.getExe pkgs.yamlfmt}";
+      options = [
+        "-formatter=retain_line_breaks_single=true"
+      ];
+      includes = [ "*.yaml" "*.yml" ];
+    };
   };
 }