GitHub Actions: ARM builds broke, workaround required

[rpavlik]

At OpenXR 1.1.43 release time:

Runners apparently now default to Windows SDK 10.0.26100.0, but are missing the corresponding ARM64 compilers.

We can force an older Windows SDK, but CMake mysteriously fails to find WindowsApp.lib on arm (32 bit) then.

So, we disabled the arm_uwp (32 bit) build, and set all the UWP builds to use WinSDK 10.0.22000.0. Should not really make any difference.

[rpavlik-bot]

An issue (number 2410) has been filed to correspond to this issue in the internal Khronos GitLab (Khronos members only: KHR:openxr/openxr#2410 ), to facilitate working group processes.

This GitHub issue will continue to be the main site of discussion.