ci: Rename `trigger` job to `build_and_test`

CI job stage `trigger` is confusing. Use obvious `build_and_test` to
indicate what happens in this stage.

Signed-off-by: Saheer Babu <saheer.babu@arm.com>

.gitlab-ci.yml

@@ -42,7 +42,7 @@ workflow:
 stages:
   - autobot
   - quality_check
-  - trigger
+  - build_and_test
 
 autobot:
   stage: autobot
@@ -92,7 +92,7 @@ license:
 
 build-test FVP:
   stage:
-    trigger
+    build_and_test
   trigger:
     include: .gitlab/ci/pipeline/pipelines_per_target/fvp.yml
     strategy: depend