ci: switch to R4.3

This is not targeting R4.1 nor R4.2.

Author: marmarek

.gitlab-ci.yml

@@ -1,9 +1,5 @@
 include:
-- file: /r4.1/gitlab-base.yml
+- file: /r4.3/gitlab-base.yml
   project: QubesOS/qubes-continuous-integration
-- file: /r4.1/gitlab-dom0.yml
-  project: QubesOS/qubes-continuous-integration
-- file: /r4.2/gitlab-base.yml
-  project: QubesOS/qubes-continuous-integration
-- file: /r4.2/gitlab-host.yml
+- file: /r4.3/gitlab-host.yml
   project: QubesOS/qubes-continuous-integration