`<yvals_core.h>`: Update `_MSVC_STL_UPDATE` to July 2023

[fsb4000]

Explanation on our wiki: Macro _MSVC_STL_UPDATE

Code:

STL/stl/inc/yvals_core.h

Line 836 in 2261f7e

#define _MSVC_STL_UPDATE 202306L

Previous issue: #3741

This issue is intended for a new contributor (especially one new to GitHub) to get started with the simplest possible change.

Please feel free to submit a pull request if there isn't one already linked here - no need to ask for permission! 😸

You can (and should) link your pull request to this issue using GitHub's close/fix/resolve syntax.
(in the PR description not the commit message)