Escape `${` in strings when printing Nix expressions

Otherwise the result of the printing can't be parsed back correctly by
Nix (because the unescaped `${` will be parsed as the begining of an
anti-quotation).

Fix #3989

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/user-envs.nix b/tests/user-envs.nix
index 1aa410cc9..43eff1a68 100644
--- a/tests/user-envs.nix
+++ b/tests/user-envs.nix
@@ -13,7 +13,7 @@ let
     builder = ./user-envs.builder.sh;
   } // {
     meta = {
-      description = "A silly test package";
+      description = "A silly test package with some \${escaped anti-quotation} in it";
     };
   });