Fix failures due to the new uniqueness validation message of variables' key

Signed-off-by: Rémy Coutable <remy@rymai.me>

ee/spec/models/ci/variable_spec.rb

@@ -6,5 +6,6 @@ describe Ci::Variable do
   it do
     is_expected.to validate_uniqueness_of(:key)
       .scoped_to(:project_id, :environment_scope)
+      .with_message(/\(\w+\) has already been taken/)
   end
 end

ee/spec/models/concerns/has_environment_scope_spec.rb

@@ -11,6 +11,7 @@ describe HasEnvironmentScope do
   it do
     is_expected.to validate_uniqueness_of(:key)
       .scoped_to(:project_id, :environment_scope)
+      .with_message(/\(\w+\) has already been taken/)
   end
 
   describe '.on_environment' do