[Bug] PDF: hyperlinks in the footer are not clickable

**Describe the bug**
I'm trying to add hyperlinks to the footer template, but when I generate a PDF, the links are not clickable.

**To Reproduce**
Steps to reproduce the behavior:
1. Add a footer.html file with the following content:
```

```
2. Set "pdfFooterTemplate": "footer.html" in "docfx.json"

**Expected behavior**
The hyperlinks in the footer should be clickable and open in a browser when clicked in the generated PDF.

**Context (please complete the following information):**
- OS: Windows 11
- Docfx version: 2.78.3

**Additional context**
Add any other context about the problem here.