zsh/direnv: Whitelist ~/mounts/.envrc explicitly

Otherwise I have to run `direnv allow` every time after the home-manager
profile changed because the link target changed.

users/simon/modules/zsh/default.nix

@@ -55,6 +55,13 @@ in
       nix-direnv = {
         enable = true;
       };
+      config = {
+        whitelist = {
+          exact = [
+            "${config.home.homeDirectory}/mounts/.envrc"
+          ];
+        };
+      };
     };
     nix-index.enable = true;
     starship = {