track addition of postResholve in nixpkgs pr 439997

This (currently-unmerged) PR adds a `postResholve` attr and
appends it to postFixup.

PR authored by dsg22 in 9bbf270466e43f2d23af34d2fff2c78c1e65c267

I will likely close that PR as soon as a I cut a resholve release
that includes this to let the bump PR supersede it.

Author: abathur

nixpkgs/resholve-utils.nix

@@ -226,6 +226,7 @@ rec {
       version,
       passthru ? { },
       solutions,
+      postResholve ? "",
       ...
     }@attrs:
     let
@@ -280,6 +281,8 @@ rec {
         # LOGLEVEL="INFO";
         preFixup = phraseSolutions solutions unresholved;
 
+        postFixup = postResholve;
+
         # don't break the metadata...
         meta = unresholved.meta;
       }