[Bug] Duplicate namespaces

**Describe the bug**
I'm trying to create a DocFX project that includes two solutions which share a number of namespaces, which results in DuplicateUids warnings being output on build and results in links to pages for shared namespaces not working properly. I've seen that the globalNamespaceId exists to get around this by assigning a unique identifier to a project so that all namespaces within it are unique, but as far as I can tell setting this property doesn't change anything.

**To Reproduce**
I have created a repo here that replicates the problem:
https://github.com/tcc-mark/DocFxGlobalNamespaceIdBug

**Expected behavior**
I would expect no DuplicateUid warnings to appear on build, and that I should be able to navigate to pages within either ProjectA or ProjectB without issue. Instead, any links that should go to ProjectB pages instead go to ProjectA.

**Context (please complete the following information):**
- OS: Windows 10
- Docfx version: 2.67.5