[WIP] changes for next release 3.11.3

[nlohmann]

This thread collects all changes made since the 3.11.2 (#3700) release.

New features

• Allow custom base class as node customization point Allow custom base class as node customization point #3110

Bug fixes

• Add missing include when JSON_DIAGNOSTICS is enabled. Compilation error with JSON_DIAGNOSTICS enabled #3717 #3717: fix compilation error: "execeptions.hpp:119 accumulate is not … #3718 Add missing <numeric> include #3719

CI

• Add a workflow to create a PR comment if the sources have not been properly formatted and amalgamated. Add 'Check amalgamation' workflow #3693
• Overwork the CI to use official images for different versions of GCC and Clang. Use official Clang/GCC containers #3703
• Add GCC 12 to the CI. Use official Clang/GCC containers #3703
• Remove cpplint from the repository and use the official pypi package instead. Use official Clang/GCC containers #3703

[nlohmann]

This post is incomplete. See the final release notes for all changes.