[clang] [clang] Fix-it hint for `++this` -> `++*this` when deref is modifiable (PR #94159)

[via cfe-commits]

Sirraide wrote:

> Also, what do you think about the fix-it hint wording for errors such as `assignment to cast is illegal, lvalue casts are not supported`?

Don’t remember what that was for off the top of my head, but just the same fix-it should be fine imo

https://github.com/llvm/llvm-project/pull/94159