ci: Add variables to the inheritance list

Extend the scope of variables for the trigger job which
creates a child pipeline.

Signed-off-by: Ali Can Ozaslan <ali.oezaslan@arm.com>

.gitlab-ci.yml

@@ -40,7 +40,11 @@ include:
 
 trigger-meta-cassini:
   inherit:
-    variables: false
+    variables:
+      - META_CASSINI_TARGET_BRANCH
+      - META_CASSINI_BUILD_IMAGE
+      - META_CASSINI_BUILD_PLATFORM
+      - META_CASSINI_FORCE_TESTS
   stage: Build
   rules:
     - !reference [".build-image:rules:skip-target-build", rules]