Fix inconsistent rendering of block mathematical expressions (#29677) (#29711)

Fix inconsistent rendering of block mathematical expressions (#29677) (#29711)

Backport #29677 by @yp05327

Fix #28735

GitHub render `\```math\``` ` as a block now.
Add `display` class will render it as a block.

After:

![image](https://github.com/go-gitea/gitea/assets/18380374/2a1c20c7-438e-4ab1-8c66-cf91c8343087)

![image](https://github.com/go-gitea/gitea/assets/18380374/b81b8a93-8bca-46a5-b7db-e0d2f53e1342)

Co-authored-by: yp05327 <576951401@qq.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>