Fixed snippet URLs for sub-folders

What does this MR do?

Updates the changes, introduced in !39960 (merged) to address the new issue #240931 (closed). Technically, we again fix the way URLs are generated when GitLab is served from a sub-folder or from the domain's root.

Since the bug is fixed in the same milestone it was introduced in, we do not need a changelog entry.

Screenshots

No visual changes

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

References #240931 (closed)