Make :minutes_cost_factor always return a float

ee/app/models/ee/ci/build.rb

@@ -37,7 +37,7 @@ module EE
 
       def shared_runners_minutes_limit_enabled?
         if ::Feature.enabled?(:ci_minutes_enforce_quota_for_public_projects)
-          project.shared_runners_minutes_limit_enabled? && runner&.minutes_cost_factor(project.visibility_level)
+          project.shared_runners_minutes_limit_enabled? && runner&.minutes_cost_factor(project.visibility_level)&.positive?
         else
           legacy_shared_runners_minutes_limit_enabled?
         end

ee/app/models/ee/ci/runner.rb

@@ -10,19 +10,19 @@ module EE
       end
 
       def minutes_cost_factor(access_level)
-        return unless instance_type?
+        return 0.0 unless instance_type?
 
         case access_level
         when ::Gitlab::VisibilityLevel::PUBLIC
-          public_projects_minutes_cost_factor if public_projects_minutes_cost_factor&.positive?
+          public_projects_minutes_cost_factor
         else # Gitlab::VisibilityLevel::PRIVATE/INTERNAL
-          private_projects_minutes_cost_factor if private_projects_minutes_cost_factor&.positive?
+          private_projects_minutes_cost_factor
         end
       end
 
       def visibility_levels_without_minutes_quota
         ::Gitlab::VisibilityLevel.options.values.reject do |visibility_level|
-          minutes_cost_factor(visibility_level)&.positive?
+          minutes_cost_factor(visibility_level).positive?
         end
       end
     end

ee/spec/models/ee/ci/runner_spec.rb

@@ -29,7 +29,7 @@ describe EE::Ci::Runner do
         context "with #{level_name}" do
           let(:visibility_level) {level_value}
 
-          it { is_expected.to be_nil }
+          it { is_expected.to eq(0.0) }
         end
       end
     end
@@ -41,7 +41,7 @@ describe EE::Ci::Runner do
         context "with #{level_name}" do
           let(:visibility_level) {level_value}
 
-          it { is_expected.to be_nil }
+          it { is_expected.to eq(0.0) }
         end
       end
     end