CI Failures on Ubuntu and Windows

[rudikershaw]

It appears that CI has been failing on all the Ubuntu actions and 2 of the Windows actions since last commit approximate 8 days ago. The commit is only a README.md change, so I suspect there has been environment changes from Github actions' side.

https://github.com/cpp-best-practices/gui_starter_template/actions/runs/2324681616

The CI failures are re-producible when you create a project using this project as a template.

[Sebanisu]

It seems like gcc 11 is loading the clang 13 headers. I'm wondering how to solve that.

The bug with msvc is due to fmt 8.1.1 triggering an odd error. Fixed in fmtlib/fmt@3e28dc0 on the master branch. For some reason msvc thinks this constexpr variable isn't being used. They changed it to const.
looks like this will be fixed in a future release of msvc as well
https://developercommunity.visualstudio.com/t/CL-version-193231328-generates-false-w/10040986