Fix fmt error in RuntimeMetrics

After fmt package was updated, some of the VELOX_CHECK_XXX fails with
"error: 'fmt::v10::detail::type_is_unformattable_for<const facebook::
velox::RuntimeCounter::Unit, char> _' has incomplete type". This commit
fixes this error in RuntimeMetrics.cpp

velox/common/base/RuntimeMetrics.cpp

@@ -41,7 +41,7 @@ void RuntimeMetric::merge(const RuntimeMetric& other)
 #endif
 #endif
 {
-  VELOX_CHECK_EQ(unit, other.unit);
+  VELOX_CHECK(unit == other.unit);
   sum += other.sum;
   count += other.count;
   min = std::min(min, other.min);