ci: Add workflow to seed cachix (#2615)

Fixes #2609.

nix/static-haskell-package.nix

@@ -59,4 +59,7 @@ let
   survey =
     import "${patched-static-haskell-nix}/survey" { inherit normalPkgs compiler defaultCabalPackageVersionComingWithGhc; };
 in
-survey.haskellPackages."${name}"
+{
+  inherit survey;
+  package = survey.haskellPackages."${name}";
+}

nix/tools/devTools.nix

@@ -303,4 +303,5 @@ buildToolbox
     hsieGraphModules
     hsieGraphSymbols
   ];
+  extra = { inherit pushCachix; };
 }