haskellPackages.shelly: fix test script execution

Due to the lack of /usr/bin/env we need to make the script executable
and throw patchShebangs against it /before/ tests are executed.

pkgs/development/haskell-modules/configuration-nix.nix

@@ -341,6 +341,14 @@ self: super: builtins.intersectAttrs super {
   gtksourceview2 = addPkgconfigDepend pkgs.gtk2 super.gtksourceview2;
   gtk-traymanager = addPkgconfigDepend pkgs.gtk3 super.gtk-traymanager;
 
+  shelly = overrideCabal (drv: {
+    # /usr/bin/env is unavailable in the sandbox
+    preCheck = drv.preCheck or "" + ''
+      chmod +x ./test/data/*.sh
+      patchShebangs --build test/data
+    '';
+  }) super.shelly;
+
   # Add necessary reference to gtk3 package
   gi-dbusmenugtk3 = addPkgconfigDepend pkgs.gtk3 super.gi-dbusmenugtk3;