Assigning a variable to itself doesn't yield a warning/error inside a closure

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Description

The logic that checks whether a variable is (mistakingly) assigned to itself is not working when the assignment is in a closure.

This currently happens with Xcode 16.3 beta 2.

Reproduction

let _ = {
    var b = false
    b = b // No warning or error
}

var a = false
a = a // Error: Assigning a variable to itself

Expected behavior

b = b should yield a warning and/or error as this code is illogical.

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.109.103 clang-1700.0.13.2)

Additional information

This looks like a silly bug, but this prevented the compiler from catching a fairly nasty bug that was hitting many customers in our apps. A functional warning would have prevented this bug from shipping in the first place.