pkg/guid is not windows specific, as it can run on Linux.
Build constraints on guid_windows and guid_nonwindows are redundant with
file names, but added for consistency.
Added missing build constraints.
Added Ubuntu to test matrix, along with windows 2022.
Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>
`golang.org/x/sys/windows.GUID` is currently only available to builds
targeting `GOOS=windows` (see golang/go#36485). This change makes it
so `windows` builds continue to use `golang.org/x/sys/windows.GUID`,
while non-`windows` builds get a different structure that has all
the same fields and methods.
Hamza El-Saawy