[Bug] Markdown table headers are not rendering correctly in extension details

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.136.1 (user setup)
- OS Version: Windows_NT x64 10.0.26200

Steps to Reproduce:

1. Open "Extensions" in the sidebar.
2. Open an extension used Markdown table in README.

## Example

Extension: AvZ (`vector-wlc.avz`)

Markdown Code:
```md
|功能|操作|
|:-:|:-:|
|查看使用教程|按下 Ctrl+Shift+P 后输入命令 `AvZ: Open Tutorial`|
```

Preview in Editor:

Display in "Extensions":

As you can see, it cannot align text within the header to the center of a column.