gitlab-ci: Don't allow Windows make job to fail

While linking is still slow (#16084) all of the correctness issues which were
preventing us from being able to enforce testsuite-green on Windows are now
resolved.

.gitlab-ci.yml

@@ -808,8 +808,6 @@ nightly-i386-windows-hadrian:
 .build-windows-make:
   extends: .build-windows
   stage: full-build
-  # due to #16084
-  allow_failure: true
   variables:
     BUILD_FLAVOUR: "quick"
     GHC_VERSION: "8.6.5"