Fix approvals UI rendering when feature is disabled

What does this MR do?

This MR updates the approvals suggestion partial to only render when the approval feature is available.

Screenshots or Screencasts (strongly suggested)

Before	After

How to setup and validate locally (strongly suggested)

@stanhu shared how to reproduce this bug in GDK in this discussion.

It appears that when the project does not have the merge request approval feature, the frontend displays this error for some reason. No backend calls are made.

Locally, I can reproduce this via:

diff --git a/ee/app/models/ee/project.rb b/ee/app/models/ee/project.rb
index 54e9224c8eff..e72786e8c489 100644
--- a/ee/app/models/ee/project.rb
+++ b/ee/app/models/ee/project.rb
@@ -376,6 +376,8 @@ def push_audit_events_enabled?
 
     override :feature_available?
     def feature_available?(feature, user = nil)
+      return false if feature == :merge_request_approvers
+
       if ::ProjectFeature::FEATURES.include?(feature)
         super
       else

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #337651 (closed)