[cxx-interop] Fix test failure on older macOS
The runtime logic for printing a foreign reference type is behind `if #available(SwiftStdlib 6.2, *)`, which means it won't run on older versions of macOS, even if you use a newer Swift runtime.
rdar://153735437
(cherry picked from commit a292113ef26429b67f01964406772ee4e266c00f)
