restinio: fix build

Test builds fail with cmake configuration error:
> string sub-command JSON failed parsing json string: * Line 1, Column 1

This is a silly regression from catch2_3 3.7.1 -> 3.8.0 bump [1].
Looks like the upstream doesn't hold catch2 correctly and overrides `main`
for this test so catch2 test discovery machinery can't work.

Upstream issue [2].

[1]: https://www.github.com/NixOS/nixpkgs/pull/371311
[2]: https://www.github.com/Stiffstream/restinio/issues/230

pkgs/by-name/re/restinio/package.nix

@@ -30,6 +30,14 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-heVdo0MtsWi/r9yse+/FZ55lhiunyEdwB3UkOOY5Vj0=";
   };
 
+  # https://www.github.com/Stiffstream/restinio/issues/230
+  # > string sub-command JSON failed parsing json string: * Line 1, Column 1
+  # > Syntax error: value, object or array expected.
+  postPatch = ''
+    substituteInPlace dev/test/CMakeLists.txt \
+      --replace-fail "add_subdirectory(metaprogramming)" ""
+  '';
+
   strictDeps = true;
 
   nativeBuildInputs = [ cmake ];