message: test: Handle test cases by reference
  Fixes a warning in XCode 12.
diff: @@ -406,7 +406,7 @@ TEST(validation, load_alignment)
  {Instr::f64_load, 3},
  };
  - for (const auto test_case : test_cases)
  + for (const auto& test_case : test_cases)
  {
  const auto instr = test_case.first;
  const auto max_align = test_case.second;
  