Only test project integrations

We have deprecated and removed the ability to create service templates,
so we can simplify this condition to only test project integrations.

app/models/integration.rb

@@ -484,7 +484,7 @@ class Integration < ApplicationRecord
   # Disable test for instance-level and group-level integrations.
   # https://gitlab.com/gitlab-org/gitlab/-/issues/213138
   def can_test?
-    !(instance_level? || group_level?)
+    project_level?
   end
 
   def project_level?

spec/models/integration_spec.rb

@@ -146,13 +146,13 @@ RSpec.describe Integration do
       subject { integration.can_test? }
 
       context 'when repository is not empty' do
-        let(:project) { build(:project, :repository) }
+        let(:project) { create(:project, :repository) }
 
         it { is_expected.to be true }
       end
 
       context 'when repository is empty' do
-        let(:project) { build(:project) }
+        let(:project) { create(:project) }
 
         it { is_expected.to be true }
       end