gitlab-ci: Try only building Windows in the quick flavour

It seems no matter how many machines I throw at Windows it's constantly behind.
Perhaps the quick build flavour will be fast enough to allow us to keep until
while we sort out our toolchain issues (#16084).
13 jobs for master in 407 minutes and 18 seconds (queued for 3 seconds)
Name Stage Failure
failed
validate-x86_64-windows Full Build
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failed
validate-aarch64-linux-deb9 Full Build
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failed
validate-x86_64-darwin Full Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
validate-x86_64-windows-hadrian Full Build
No job log