No error about repeated keyword argument

Consider this code:

def f(**kwargs: object) -> None: ...
f(a=1, a=2) # no errors here

Expected Behavior
Error from mypy like this: SyntaxError: keyword argument repeated: a

Actual Behavior
At runtime:

  File "<some_file>", line 27
    f(a=1, a=2)
           ^^^
SyntaxError: keyword argument repeated: a

Mypy's output:

>mypy file.py
Success: no issues found in 1 source file

Your Environment

• Mypy version used: mypy 1.0.0+dev.154fee110f274fe6214eff856b65d437ee299fdb (compiled: no) (I did pip install -U git+https://github.com/python/mypy.git several minutes ago)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32

Reproduce the issue with the Python snippet and mypy command shown in the report. Trace how mypy processes calls with repeated keyword arguments and locate the existing diagnostic tests for call expressions. Done means mypy reports an error for the duplicate keyword while preserving normal handling of **kwargs.