gitlab-ci: Declare needs: for stretch docker image

This allows the *-old-llvm jobs to run before the buster docker images
are ready.

v2:
* Use - list syntax instead of [] (Eric Engestrom)

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
1 file changed