warn_unreachable fails in trivial cases since 0.920 #11796

Bug Report

In a trivial case (see below) where warn_unreachable = True results in an error up to and including 0.910, 0.920 does not.

To Reproduce

mypy.ini:

[mypy]
warn_unreachable = True

test.py:

def foo():
    return
    unreachable = 1

run mypy test.py --config-file mypy.ini
Expected Behavior

test.py:3: error: Statement is unreachable
Found 1 error in 1 file (checked 1 source file)

Actual Behavior

Success: no issues found in 1 source file

Your Environment

• Mypy version used: 0.920
• Mypy command-line flags: --config-file
• Mypy configuration options from mypy.ini (and other config files): warn_unreachable = True
• Python version used: 3.9.9
• Operating system and version: Manjaro