build: switch to C++20

Per [1], we should be building with the latest C++ version.  C++20
has been final and approved for over 6 months now, so it is about
time for us to switch.

1. https://github.com/openbmc/docs/blob/master/cpp-style-and-conventions.md#code-should-be-written-with-modern-practices

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iefbe930f9da1d134696aaec18949b2ac1d956f99
diff --git a/test/utility/type_traits.cpp b/test/utility/type_traits.cpp
index 0a61648..e1e9473 100644
--- a/test/utility/type_traits.cpp
+++ b/test/utility/type_traits.cpp
@@ -60,7 +60,7 @@
     using namespace testing;
 
     // std::map has member_contains from c++20
-    ASSERT_THAT((has_member_contains_v<std::map<std::string, int>>), Eq(false));
+    ASSERT_THAT((has_member_contains_v<std::map<std::string, int>>), Eq(true));
     ASSERT_THAT(
         (has_member_contains_v<std::vector<std::pair<std::string, int>>>),
         Eq(false));