Use auto instead of a type

Change-Id: I5167bf7fca91b25adccd87f802a6bff87723d427
diff --git a/tests/pretty_printers.hpp b/tests/pretty_printers.hpp
index 5b747a1..65e28a6 100644
--- a/tests/pretty_printers.hpp
+++ b/tests/pretty_printers.hpp
@@ -180,7 +180,7 @@
             s << "Absolute::End";
         }
     } else {
-        const yang::move::Relative& relative = std::get<yang::move::Relative>(move.m_destination);
+        const auto& relative = std::get<yang::move::Relative>(move.m_destination);
         s << "Relative {\n";
         s << "        position: ";
         if (relative.m_position == yang::move::Relative::Position::After) {