fix CI trying to run builds using 'dunfell' release

.gitlab-ci.yml

@@ -2,6 +2,7 @@ variables:
   META_OST_BRANCH: ${CI_COMMIT_BRANCH}
   REPO_YOCTO_URL: https://git.toradex.com/toradex-manifest.git
   REPO_YOCTO_OPTS: -b refs/tags/5.4.0 -m tdxref/default.xml
+  YOCTO_BRANCH: kirkstone
 
 
 include:
@@ -35,15 +36,8 @@ include:
 
 .rules_cb20:
   rules:
-  - if: '$BUILD_MACHINES_OVERRIDE =~ /^.*cb20.*$/'
+  - if: $YOCTO_BRANCH == "dunfell"
     when: on_success
-  - if: $GIT_COMMIT_MESSAGE =~ /^\[skip\s*cb20\s*\].*$/
-    when: never
-  - if: $GIT_COMMIT_MESSAGE =~ /^\[only\s*cb20\s*\].*$/
-    when: on_success
-  - if: $GIT_COMMIT_MESSAGE =~ /^\[only.*\].*$/
-    when: never
-  - when: on_success
 
 build_cb20:
   extends: .repo-image