Move libsodium fix into test/overlay.nix

Author: hamishmack

ci.nix

@@ -29,12 +29,9 @@
       (final: prev: {
         haskell-nix = prev.haskell-nix // {
           inherit checkMaterialization;
-          extraPkgconfigMappings = prev.haskell-nix.extraPkgconfigMappings or {} // {
-            "libsodium" = [ "libsodium-18" ];
-          };
         };
-        libsodium-18 = (final.callPackage (inputs.nixpkgs-2311 + "/pkgs/development/libraries/libsodium") {}).overrideAttrs (_: { dontDisableStatic = true; });
       })
+      (import ./test/overlay.nix)
     ];
     # Needed for dwarf tests
     config = haskellNix.config // {

test/overlay.nix

@@ -0,0 +1,8 @@
+final: prev: {
+  haskell-nix = prev.haskell-nix // {
+    extraPkgconfigMappings = prev.haskell-nix.extraPkgconfigMappings or {} // {
+      "libsodium" = [ "libsodium-18" ];
+    };
+  };
+  libsodium-18 = (final.callPackage (final.haskell-nix.sources.nixpkgs-2311 + "/pkgs/development/libraries/libsodium") {}).overrideAttrs (_: { dontDisableStatic = true; });
+}