async: proxy: use variant in property-set

The DBus.Properties.Set method doesn't take a raw type, but a variant
holding the type (just like Get returns a variant).  Fix the function
call so that the set value is wrapped in a variant.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3d33e0539c008dd66feeef0b866911768dae84e2
diff --git a/include/sdbusplus/async/proxy.hpp b/include/sdbusplus/async/proxy.hpp
index 2be9b38..be006dd 100644
--- a/include/sdbusplus/async/proxy.hpp
+++ b/include/sdbusplus/async/proxy.hpp
@@ -195,8 +195,9 @@
         requires((S) && (P) && (I))
     {
         auto prop_intf = proxy(s, p, dbus_prop_intf);
-        return prop_intf.template call<>(ctx, "Set", c_str(i), property.data(),
-                                         std::forward<T>(value));
+        return prop_intf.template call<>(
+            ctx, "Set", c_str(i), property.data(),
+            std::variant<std::decay_t<T>>{std::forward<T>(value)});
     }
 
   private: