Improve small things

spec/models/ci/variable_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Ci::Variable, models: true do
   subject { build(:ci_variable) }
 
-  it { is_expected.to be_kind_of(HasVariable) }
+  it { is_expected.to include_module(HasVariable) }
   it { is_expected.to validate_uniqueness_of(:key).scoped_to(:project_id) }
 
   describe '.unprotected' do

spec/models/concerns/has_variable_spec.rb

@@ -3,8 +3,6 @@ require 'spec_helper'
 describe HasVariable do
   subject { build(:ci_variable) }
 
-  let(:secret_value) { 'secret' }
-
   it { is_expected.to validate_presence_of(:key) }
   it { is_expected.to validate_length_of(:key).is_at_most(255) }
   it { is_expected.to allow_value('foo').for(:key) }
@@ -13,7 +11,7 @@ describe HasVariable do
 
   describe '#value' do
     before do
-      subject.value = secret_value
+      subject.value = 'secret'
     end
 
     it 'stores the encrypted value' do