nixos/tests/gitlab: Fix Authorization Bearer field

Due to an incorrect shell escape the Authorization Bearer Token was not
present in the cURL request headers.

nixos/tests/gitlab.nix

@@ -112,7 +112,7 @@ import ./make-test-python.nix ({ pkgs, lib, ...} : with lib; {
             "${pkgs.sudo}/bin/sudo -u gitlab -H gitlab-rake gitlab:check 1>&2"
         )
         gitlab.succeed(
-            "echo \"Authorization: Bearer \$(curl -X POST -H 'Content-Type: application/json' -d @${auth} http://gitlab/oauth/token | ${pkgs.jq}/bin/jq -r '.access_token')\" >/tmp/headers"
+            "echo \"Authorization: Bearer $(curl -X POST -H 'Content-Type: application/json' -d @${auth} http://gitlab/oauth/token | ${pkgs.jq}/bin/jq -r '.access_token')\" >/tmp/headers"
         )
       '' + optionalString doSetup ''
         gitlab.succeed(