Refresh service_account_token for kubernetes_namespaces

There seems to be several examples where service_account_token is blank
even in GitLab.com newly created kubernetes_namespaces . We have not
figured out why they are blank but this should hopefully fix some issues
similar to https://gitlab.com/gitlab-org/gitlab-ce/issues/55362

changelogs/unreleased/55362-refresh-blank-service-account-token.yml

+---
+title: Refresh service_account_token for kubernetes_namespaces
+merge_request: 29657
+author:
+type: fixed

lib/gitlab/ci/build/prerequisite/kubernetes_namespace.rb

@@ -9,7 +9,7 @@ module Gitlab
             deployment_cluster.present? &&
               deployment_cluster.managed? &&
               !deployment_cluster.project_type? &&
-              kubernetes_namespace.new_record?
+              (kubernetes_namespace.new_record? || kubernetes_namespace.service_account_token.blank?)
           end
 
           def complete!

spec/factories/clusters/kubernetes_namespaces.rb

@@ -16,5 +16,9 @@ FactoryBot.define do
     trait :with_token do
       service_account_token { FFaker::Lorem.characters(10) }
     end
+
+    trait :without_token do
+      service_account_token nil
+    end
   end
 end

spec/lib/gitlab/ci/build/prerequisite/kubernetes_namespace_spec.rb

@@ -35,9 +35,15 @@ describe Gitlab::Ci::Build::Prerequisite::KubernetesNamespace do
         end
 
         context 'and a namespace is already created for this project' do
-          let!(:kubernetes_namespace) { create(:cluster_kubernetes_namespace, cluster: cluster, project: build.project) }
+          let!(:kubernetes_namespace) { create(:cluster_kubernetes_namespace, :with_token, cluster: cluster, project: build.project) }
 
           it { is_expected.to be_falsey }
+
+          context 'and the service_account_token is blank' do
+            let!(:kubernetes_namespace) { create(:cluster_kubernetes_namespace, :without_token, cluster: cluster, project: build.project) }
+
+            it { is_expected.to be_truthy }
+          end
         end
 
         context 'and cluster is project type' do