ci: Allow msys2 jobs to fail

The msys2 runner has started failing for internal reasons:

 - gtk-3-24 times out
 - master fails with a ld.exe assertion:
   BFD (GNU Binutils) 2.33.1 assertion fail
   ../../binutils-2.33.1/bfd/cofflink.c:2348

Both seem related to some MSYS2 issue. Until the runner is updated, we
should not block on it.

.gitlab-ci.yml

@@ -40,6 +40,7 @@ fedora-x86_64:
   script:
     - C:\msys64\usr\bin\pacman --noconfirm -Syyuu
     - C:\msys64\usr\bin\bash -lc "bash -x ./.gitlab-ci/test-msys2.sh"
+  allow_failure: true
   cache:
     key: "%CI_JOB_NAME%"
     <<: *cache-paths