Set ENV var to allow CI jobs to run decomposed

We run CI with decomposed databases so we need to set this env var to
bypass our safety checks when some jobs run in production mode

.gitlab-ci.yml

@@ -155,6 +155,7 @@ variables:
   RETRY_FAILED_TESTS_IN_NEW_PROCESS: "true"
   # Run with decomposed databases by default
   DECOMPOSED_DB: "true"
+  GITLAB_ALLOW_SEPARATE_CI_DATABASE: "true"
 
   DOCS_REVIEW_APPS_DOMAIN: "docs.gitlab-review.app"
   DOCS_GITLAB_REPO_SUFFIX: "ee"

.gitlab/ci/memory.gitlab-ci.yml

@@ -26,7 +26,6 @@ memory-on-boot:
     NODE_ENV: "production"
     RAILS_ENV: "production"
     SETUP_DB: "true"
-    GITLAB_ALLOW_SEPARATE_CI_DATABASE: "true"
     MEMORY_ON_BOOT_FILE_PREFIX: "tmp/memory_on_boot_"
     TEST_COUNT: 5
   script:

spec/initializers/check_forced_decomposition_spec.rb

@@ -7,6 +7,10 @@
     load Rails.root.join('config/initializers/check_forced_decomposition.rb')
   end
 
+  before do
+    stub_env('GITLAB_ALLOW_SEPARATE_CI_DATABASE', nil)
+  end
+
   context 'for production env' do
     before do
       allow(Gitlab).to receive(:dev_or_test_env?).and_return(false)