lib: add modules.mkTestOverride

nix/lib/default.nix

@@ -8,6 +8,8 @@ libO
 
   # groups
 
+  modules = libO.modules // lib.importFlakeMod ./modules.nix;
+
   types = libO.types // lib.importFlakeMod ./types.nix;
 
   x-banananetwork-unused = lib.importFlakeMod ./unused.nix;

nix/lib/modules.nix

@@ -0,0 +1,9 @@
+{ lib, ... }@flakeArg:
+let
+  inherit (lib.modules) mkOverride;
+in
+{
+
+  mkTestOverride = mkOverride 55;
+
+}