register_checks: pass geometry context by reference instead of passing by value

If we pass by value then the context gets eventually delivered to single_store
in a broken state

Author: Vakho Tsulaia

tests/include/detray/test/common/detail/register_checks.hpp

@@ -20,7 +20,7 @@ template <template <typename> class check_t, typename detector_t,
 void register_checks(const detector_t &det,
                      const typename detector_t::name_map &vol_names,
                      const config_t &cfg = {},
-                     const typename detector_t::geometry_context gctx = {}) {
+                     const typename detector_t::geometry_context& gctx = {}) {
 
     const char *test_name = cfg.name().c_str();
     if (!test_name) {