Simplify CI_DEPLOY_FREEZE conditions in Auto DevOps

There's no need to compare against null, because null is a falsy value
in rules:if.

See https://gitlab.com/gitlab-org/gitlab/-/issues/351928

Changelog: changed

lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml

@@ -103,7 +103,7 @@ canary:
     name: production
     url: http://$CI_PROJECT_PATH_SLUG.$KUBE_INGRESS_BASE_DOMAIN
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -135,7 +135,7 @@ canary:
 production:
   <<: *production_template
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -153,7 +153,7 @@ production_manual:
   <<: *production_template
   allow_failure: false
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -192,7 +192,7 @@ production_manual:
   resource_group: production
   allow_failure: true
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -207,7 +207,7 @@ production_manual:
 .timed_rollout_template: &timed_rollout_template
   <<: *rollout_template
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never

lib/gitlab/ci/templates/Jobs/Deploy.latest.gitlab-ci.yml

@@ -103,7 +103,7 @@ canary:
     name: production
     url: http://$CI_PROJECT_PATH_SLUG.$KUBE_INGRESS_BASE_DOMAIN
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -135,7 +135,7 @@ canary:
 production:
   <<: *production_template
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -153,7 +153,7 @@ production_manual:
   <<: *production_template
   allow_failure: false
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -192,7 +192,7 @@ production_manual:
   resource_group: production
   allow_failure: true
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never
@@ -207,7 +207,7 @@ production_manual:
 .timed_rollout_template: &timed_rollout_template
   <<: *rollout_template
   rules:
-    - if: '$CI_DEPLOY_FREEZE != null'
+    - if: '$CI_DEPLOY_FREEZE'
       when: never
     - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never

spec/lib/gitlab/ci/templates/Jobs/deploy_gitlab_ci_yaml_spec.rb

@@ -66,6 +66,11 @@ RSpec.describe 'Jobs/Deploy.gitlab-ci.yml' do
           expect(build_names).not_to include('review')
         end
 
+        it 'when CI_DEPLOY_FREEZE is present' do
+          create(:ci_variable, project: project, key: 'CI_DEPLOY_FREEZE', value: 'true')
+          expect(build_names).to eq %w(placeholder)
+        end
+
         it 'when CANARY_ENABLED' do
           create(:ci_variable, project: project, key: 'CANARY_ENABLED', value: 'true')