Attempt to make the FlakeRef test succeed on macOS

Author: edolstra

src/libflake-tests/flakeref.cc

@@ -8,6 +8,8 @@ namespace nix {
 /* ----------- tests for flake/flakeref.hh --------------------------------------------------*/
 
     TEST(parseFlakeRef, path) {
+        experimentalFeatureSettings.experimentalFeatures.get().insert(Xp::Flakes);
+
         fetchers::Settings fetchSettings;
 
         {

src/libutil/config.hh

@@ -262,6 +262,7 @@ public:
     operator const T &() const { return value; }
     operator T &() { return value; }
     const T & get() const { return value; }
+    T & get() { return value; }
     template<typename U>
     bool operator ==(const U & v2) const { return value == v2; }
     template<typename U>