[1.77][multi_index] post-beta merge request

From: Joaquin M López Muñoz (joaquinlopezmunoz_at_[hidden])
Date: 2021-07-16 06:31:37

Hi,

I'd like to merge this commit (only testing code and docs affected):

https://github.com/boostorg/multi_index/commit/3dad7f38a44783c297b2d477cba21a1a96538ca0

This is a trivial change for C++23 forward compatibility (and C++<23 UB 
avoidance), as explained in

https://github.com/boostorg/multi_index/issues/45

Best,

Joaquín M López Muñoz