ci: Condition Windows containers on Windows rules
The Windows container is not necessary for changes that do not affect Windows. As only a small number of Mesa drivers run on Windows, this means that most hardware driver-specific changes can skip the Windows container build.
Last night there was an infrastructure issue external to us causing the Windows container builds to timeout. While this would not have fixed that or helped with common code MRs, at least it would've let me merge Panfrost code in the mean time ;-)
Cc @daniels