Format .nix files

This does not include any automation for the release branch, but
is based on the configuration of https://github.com/NixOS/nix/pull/12349

    pre-commit run -a nixfmt-rfc-style

tests/functional/lang/eval-okay-list.nix

@@ -2,6 +2,11 @@ with import ./lib.nix;
 
 let {
 
-  body = concat ["foo" "bar" "bla" "test"];
-    
-}
+  body = concat [
+    "foo"
+    "bar"
+    "bla"
+    "test"
+  ];
+
+}