gitlab-ci/cirrus: switch from 'master' to 'latest'

Commit ab72522 "gitlab: switch from 'stable' to
'latest' docker container tags" switched most tags
to 'latest' but missed cirrus image.  Fix this now.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2256
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Message-id: 20240401051633.2780456-1-mjt@tls.msk.ru
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 1d2f2b3)

.gitlab-ci.d/cirrus.yml

@@ -13,7 +13,7 @@
 .cirrus_build_job:
   extends: .base_job_template
   stage: build
-  image: registry.gitlab.com/libvirt/libvirt-ci/cirrus-run:master
+  image: registry.gitlab.com/libvirt/libvirt-ci/cirrus-run:latest
   needs: []
   timeout: 80m
   allow_failure: true