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).
16 jobs for master in 478 minutes and 29 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Lint
passed #6412
lint
ghc-linters

00:01:17

 
  Build
failed #6413
x86_64-linux allowed to fail
validate-x86_64-linux-deb8-hadrian

01:01:14

passed #6414
x86_64-linux
validate-x86_64-linux-deb9

01:14:15

 
  Full Build
failed #6416
aarch64-linux allowed to fail
validate-aarch64-linux-deb9

03:04:49

passed #6417
x86_64-linux
validate-i386-linux-deb9

01:06:47

failed #6415
x86_64-darwin allowed to fail
validate-x86_64-darwin

01:24:58

passed #6419
x86_64-linux
validate-x86_64-linux-deb8

01:10:32

failed #6421
x86_64-linux
validate-x86_64-linux-deb9-integer-simple

01:11:00

passed #6418
x86_64-linux
validate-x86_64-linux-deb9-llvm

02:16:02

passed #6422
x86_64-linux
validate-x86_64-linux-deb9-unreg

02:13:29

passed #6420
x86_64-linux
validate-x86_64-linux-fedora27

01:10:13

failed #6641
x86_64-windows allowed to fail
validate-x86_64-windows

00:00:00

failed #6642
x86_64-windows allowed to fail
validate-x86_64-windows-hadrian

00:00:00

failed #6424
x86_64-windows allowed to fail
validate-x86_64-windows

00:00:04

failed #6637
x86_64-windows allowed to fail
validate-x86_64-windows

02:42:54

failed #6423
x86_64-windows allowed to fail
validate-x86_64-windows-hadrian

00:00:04

 
Name Stage Failure
failed
validate-x86_64-linux-deb8-hadrian Build
No job log
failed
validate-x86_64-darwin Full Build
No job log
failed
validate-x86_64-linux-deb9-integer-simple Full Build
No job log
failed
validate-x86_64-windows-hadrian Full Build
No job log
failed
validate-x86_64-windows Full Build
No job log
failed
validate-aarch64-linux-deb9 Full Build
No job log