Ensure subject passes validations

Rails 5 requires that belongs_to associations have the associated record
present. These tests were failing because they had nil values.

spec/models/ci/pipeline_schedule_spec.rb

@@ -3,6 +3,8 @@
 require 'spec_helper'
 
 describe Ci::PipelineSchedule do
+  subject { build(:ci_pipeline_schedule) }
+
   it { is_expected.to belong_to(:project) }
   it { is_expected.to belong_to(:owner) }
 

spec/models/clusters/cluster_spec.rb

@@ -5,6 +5,8 @@ require 'spec_helper'
 describe Clusters::Cluster do
   it_behaves_like 'having unique enum values'
 
+  subject { build(:cluster) }
+
   it { is_expected.to belong_to(:user) }
   it { is_expected.to have_many(:cluster_projects) }
   it { is_expected.to have_many(:projects) }