ci: Fix trigger rules
requested to merge Ali.Oezaslan/meta-cassini-bsp:topics/CAS-84/AMPLATFORMS-3087-fix-rules into nanbield
The META_CASSINI_PROJECT and META_CASSINI_TARGET_BRANCH variables are checked to see which ones are empty. However, since these are not defined variables, they also need a null check.
CI_MERGE_REQUEST_IID only gets a unique value in the merge request.
Signed-off-by: Ali Can Ozaslan ali.oezaslan@arm.com