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/failing.nix

@@ -2,16 +2,29 @@
 with import ./config.nix;
 let
 
-  mkDerivation = args:
-    derivation ({
-      inherit system;
-      builder = busybox;
-      args = ["sh" "-e" args.builder or (builtins.toFile "builder-${args.name}.sh" ''
-        if [ -e "$NIX_ATTRS_SH_FILE" ]; then source $NIX_ATTRS_SH_FILE; fi;
-        eval "$buildCommand"
-      '')];
-    } // removeAttrs args ["builder" "meta"])
-    // { meta = args.meta or {}; };
+  mkDerivation =
+    args:
+    derivation (
+      {
+        inherit system;
+        builder = busybox;
+        args = [
+          "sh"
+          "-e"
+          args.builder or (builtins.toFile "builder-${args.name}.sh" ''
+            if [ -e "$NIX_ATTRS_SH_FILE" ]; then source $NIX_ATTRS_SH_FILE; fi;
+            eval "$buildCommand"
+          '')
+        ];
+      }
+      // removeAttrs args [
+        "builder"
+        "meta"
+      ]
+    )
+    // {
+      meta = args.meta or { };
+    };
 in
 {