Classmethod bound with an additional name trigger stubtest errors #15717

Bug Report

Classmethods bound with an additional name trigger stubtest errors.

To Reproduce

Consider the following trivial module and companion typing stub file

# mod.py
class T:
    def a(self): pass
    b = a
    @classmethod
    def c(cls): pass
    d = c

# mod.pyi
class T:
    def a(self) -> None: pass
    b = a
    @classmethod
    def c(cls) -> None: pass
    d = c

then run stubtest the following way:

PYTHONPATH=$PWD stubtest mod

Expected Behavior

stubtest succeeds with no output printed

Actual Behavior

error: mod.T.d variable differs from runtime type def () -> Any
Stub: in file /home/dalcinl/tmp/pkg/mod.pyi:6
def (cls: Type[mod.T])
Runtime: in file /tmp/mod.py:4
<bound method T.c of <class 'mod.T'>>

Found 1 error (checked 1 module)

Please note that the issue comes from a @classmethod, a regular method does not trigger the error.

Your Environment

• Mypy version used: 1.4.1
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11.4