ci: add a 10min job timeout to formatting checks

They both take only a few seconds, but it can take up to a minute for
setting up the job, and various external factors such as network can add
delays, so let's round it up to a generous 10 minutes.

Signed-off-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24431>

.gitlab-ci/test/gitlab-ci.yml

@@ -30,6 +30,7 @@
     - allow_failure: true
   variables:
     GIT_STRATEGY: fetch
+  timeout: 10m
   script:
     - git diff --color=always --exit-code  # Fails if there are diffs