Annotations in typing.Annotated are not checked #10872

Bug Report

To Reproduce

import typing_extensions as te
x: te.Annotated[int, Foobar] = 42

Expected Behavior

Mypy complains about Foobar not being defined. In other cases, e.g. when a function is called in an Annotated argument, it checks if the arguments passed to the function are valid (or number of arguments match, etc. etc.).

Actual Behavior

Mypy does not complain about Foobar not being defined.

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: 3.8.2
• Operating system and version: OSX