[clang-tools-extra] [clang] [clang-tidy] fix misc-const-correctnes false-positive for fold expressions (PR #78320)

[Julian Schmidt via cfe-commits]

5chmidti wrote:

@PiotrZSL is this a reconfirmation of your previous approval (given the changed tests and release note), or is this an approval for everything?
Specifically
> LGTM, but i'm not 100% sure about ExprMutationAnalyzer part (if thats a right place).
> Leave it open for few days, so others could comment if they have objections.

(I think it is the right place, just under the `binaryOperator` which is incredibly similar to the case detected by the `cxxFoldExpr` matcher)

https://github.com/llvm/llvm-project/pull/78320