ci: Ensure layer-checks are run on scheduled builds

The yocto layer-check should be run on manual, scheduled and MR builds but not on push commits due to them taking a large amount of processing power. By moving up to the latest GitLab templates we have access to a variable that contains the reason a parent pipeline was triggered, we now use this variable within the child pipeline to determine if the layer-checks should be run or not.

Changelog: bug Signed-off-by: Drew Reed Drew.Reed@arm.com