[clang-tools-extra] [llvm] [clang-tools-extra][docs] Use Furo theme to match clang (PR #222196)

[Reid Kleckner via cfe-commits]

rnk wrote:

> Hm, I suppose some tests broke because we compare current version of list.md against "auto generated" one. We should either disable test or fix it. The test asserts that the check table is properly sorted

Fixed, sorry, I just validated by building the docs and checking the appearance, not by running the tests locally.

https://github.com/llvm/llvm-project/pull/222196