build(lib{expr,store,util}-test-support): depend on -c libraries

Since lib{expr,store,util}-test-support subprojects define nix_api_* helpers
for testing nix c bindings, they need to publicly depend on -c counterparts.
This makes their headers self-sufficient and does not rely on the -tests to add
necessary dependencies.

src/libutil-test-support/package.nix

@@ -3,6 +3,7 @@
 , mkMesonLibrary
 
 , nix-util
+, nix-util-c
 
 , rapidcheck
 
@@ -33,6 +34,7 @@ mkMesonLibrary (finalAttrs: {
 
   propagatedBuildInputs = [
     nix-util
+    nix-util-c
     rapidcheck
   ];