Resolve "Double Horizontal Line on New Issue"

What does this MR do?

This MR just moves the hr that goes between the branch chooser and the rest of the form into the template for the branch chooser.

That way, if the branch chooser isn't displayed (e.g. in the New Issue page), neither is the hr.

Screenshots

	Updated	Previous
New Issue
New Merge Request
Edit Merge Request

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• ~~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

Closes #36418 (closed)