fix: GitLab-CI YAML syntax

.gitlab-ci.yml

@@ -20,7 +20,7 @@ test-job-debian12:
   stage: test
   tags:
     - "shell"
-  vars:
+  variables:
     SCENARIO: "virtualbox_debian12"
   script:
     # make sure that Ansible Vaults are present and can be decrypted
@@ -45,7 +45,7 @@ test-job-alma8:
   stage: test
   tags:
     - "shell"
-  vars:
+  variables:
     SCENARIO: "virtualbox_alma8"
   script:
     # make sure that Ansible Vaults are present and can be decrypted