cpp: bump desired C++ standard to C++20

C++20 has been final for over 6 months now and has sufficient
compiler support in the compilers we use.  Bump the documentation
to specify we should be using C++20 now.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1917b24a8e225393daf81249ce1ab8e804882eef
diff --git a/cpp-style-and-conventions.md b/cpp-style-and-conventions.md
index 9e8fc2d..473f4b5 100644
--- a/cpp-style-and-conventions.md
+++ b/cpp-style-and-conventions.md
@@ -33,8 +33,8 @@
 ### Code should be written with modern practices
 
 We strive to keep our code conforming to and utilizing of the latest in C++
-standards.  Today, that means all C++ code should be compiled using C++17
-compiler settings.  As the C++20 standard is finalized and compilers support
+standards.  Today, that means all C++ code should be compiled using C++20
+compiler settings.  As the C++23 standard is finalized and compilers support
 it, we will move to it as well.
 
 We also strive to keep the codebase up-to-date with the latest recommended