[Bug] Shorthand Links are not checked for broken links

When using shorthand links such es `@versionhistorx` this link is not checked if is broken.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a file `versionhistory.md`
2. Set the `uid: versionhistory` in the content
3. Create another file `reference.md`
4. In this file create the following:

```
## Sample
@versionhistory
@versionhistorx


```

**Expected behavior**
Using `` will lead to warning, when the target does not exist:
`warning UidNotFound: 1 invalid cross reference(s) , "versionhistorx".`
This behavior would be expected as well, when using `@versionhistorx` which is not the case.

**Context:**
- OS: Windows 10
- Docfx version: 2.76.0