Port PR from PBS-Java: Yieldlab: Fix the default endpoint

[cross-repo-issue-creation[bot]]

A PR was merged over on PBS-Java

• https://github.com/prebid/prebid-server-java/pull/3021
• timestamp: 2024-03-12T15:34:51Z

[bsardo]

PBS-Go does not have the issue Java was experiencing with double slashes but we can make the URL match what is in Java for consistency.