[clang-tidy] fix match for binaryOperator in ExprMutationAnalyzer for...

[clang-tidy] fix match for binaryOperator in ExprMutationAnalyzer for misc-const-correctness (#70559)

The `ExprMutationAnalyzer`s matcher of `binaryOperator`s
that contained the variable expr, were previously narrowing the
variable to be type dependent, when the `binaryOperator` should
have been narrowed as dependent.
The variable we are trying to find mutations for does
not need to be the dependent type, the other operand of
the `binaryOperator` could be dependent.

Fixes #57297