ci/build: debian-build-testing should follow same limit as other jobs

This was temporarily measure to prevent long LTO builds get stuck.

Signed-off-by: David Heidelberg <david@ixit.cz>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31758>

.gitlab-ci/build/gitlab-ci.yml

@@ -215,7 +215,6 @@ debian-build-testing:
   script: |
     .gitlab-ci/meson/build.sh
     .gitlab-ci/prepare-artifacts.sh
-  timeout: 15m
 
 shader-db:
   stage: code-validation