Class definition scope using walrus assignment operator raises [name-defined] error

Bug Report

When using the assignment operator (aka "walrus") inside the class definition scope, I get a [name-defined] error.

To Reproduce
https://mypy-play.net/?mypy=latest&python=3.11&gist=367470bba328790329e68ce08bd7eb59

class TestTuple:
    t = (a := 1, a)


class TestExpression:
    (b := 2, b)


def add(x: int, y: int):
    return x + y


class TestAdd:
    result = add(c := 3, c)


class TestOverride:
    d = add(d := 4, d)


TestTuple.a      # output: 1
TestTuple.t      # output: (1, 1)
TestExpression.b # output: 2
TestAdd.c        # output: 3
TestAdd.result   # output: 6
TestOverride.d   # output: 8

Expected Behavior
I expected mypy to not raise any error as these all execute in python.

Actual Behavior

main.py:2: error: Name "a" is not defined  [name-defined]
main.py:6: error: Name "b" is not defined  [name-defined]
main.py:14: error: Name "c" is not defined  [name-defined]
main.py:18: error: Name "d" is not defined  [name-defined]
Found 4 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.6.1
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.11

リンクされている mypy-play の再現例と、issue 内の Python 3.11 の例から始め、その後、クラススコープの walrus 代入がどのように解析されるかを追跡します。報告された例が、示されている推論値を維持したまま、4 件の name-defined エラーなしで型チェックを通れば完了です。