attempt to get `.#cabal-test` to work on ci

flake.nix

@@ -87,6 +87,12 @@
               cat >cabal.project.local <<EOF
               -- This file is auto-generated by the flake devShell's shellHook.  Do
               -- not edit this file.  Make changes in flake.nix.
+              package zlib
+                -- by default the cabal build won't use pkg-config to find the
+                -- underlying zlib c library.  this will most likely cause
+                -- "cabal build" to fail (unless other steps are taken).  turn
+                -- on pkg-config so that the cabal-test app below can succeed.
+                flags: -bundled-c-zlib -non-blocking-ffi +pkg-config
               EOF
             '';
           }