[clang-tools-extra] [clang-tidy] [docs] Replace _not_ in reserved-identifier.rst with *not* (PR #112162)

[Carlos Galvez via cfe-commits]

carlosgalvezp wrote:

@njriasan Thanks for the contribution! I see the commit message would include this:

```
Co-authored-by: Nicholas Riasanovsky <nicholasriasanovsky at macbook-pro.myfiosgateway.com>
```

Do you want to keep that?

https://github.com/llvm/llvm-project/pull/112162