Fix relative URL root in wiki_base_path

Merged Markus Koller requested to merge 218823-wiki-base-path-relative-url-root into master

What does this MR do?

This was a bug introduced in fe5533a7.

Previously we were building the path manually and had to also include Gitlab.config.gitlab.relative_url_root, but since we're using route helpers now it's already included via default_url_options, which resulted in a duplicated root in the URL.

Addresses #218823 (closed) and #220036 (closed).

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

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
Edited by Markus Koller