docker-image template should use docker-privileged-xl runner tag

https://cern.service-now.com/service-portal?id=outage&n=OTG0078219 requires the docker-privileged jobs to be run on docker-privileged-xl runners.

I would contribute an MR, but I don't have perms to push. Here's a patch:

diff --git a/docker-image.gitlab-ci.yml b/docker-image.gitlab-ci.yml
index f984d65..5fc3e10 100644
--- a/docker-image.gitlab-ci.yml
+++ b/docker-image.gitlab-ci.yml
@@ -27,7 +27,9 @@ variables:
   stage: build
   # This job should only be taken by the privileged runners.
   tags:
-    - docker-privileged
+    # OTG0078219 requires docker-privileged jobs
+    # are run on docker-privileged-xl runners.
+    - docker-privileged-xl
   services:
     - docker:20.10.17-dind
   script: