Fix stale wiki link in patching docs (#35000)

The wiki content was moved into the docs folder, so the external
link to brave-browser/wiki/Patching-Chromium#making-methods-virtual
now just redirects. Use a local anchor instead.

docs/patching_and_chromium_src.md

@@ -23,7 +23,7 @@ To change an upstream logic it's often best to simply subclass a Chromium class,
 You will need to patch (see the below documentation) for some small trivial things in this case:
 - Create instances of your class instead of the Chromium class.
 - Possibly add a `friend` member to the base class you're subclassing.
-- Possibly add a `virtual` keyword to functions you'd like to subclass - [example](https://github.com/brave/brave-browser/wiki/Patching-Chromium#making-methods-virtual)
+- Possibly add a `virtual` keyword to functions you'd like to subclass - [example](#making-methods-virtual)
 
 Header patches should use preprocessor defines when possible. The define should always be the last thing in `public` so you can change to `protected` or `private` inside the define.
 ```