Don't require type annotations for locals when using --check-untyped-defs

[rggjan]

Trying to reopen or clone #7744 but didn't figure out how, so I created a new issue instead.

See #7744 for all the required information.

[JukkaL]

The issue is about cases like this, which currently generate an error:

def foo():
    data = { # error: Need type annotation for 'data'
        'abc': {}
    }

I think that not generating an error here should just be the default behavior. This would be a logical continuation of changes introduced in #7530.

[JukkaL]

@msullivan @ilevkivskyi Do you agree with me?

[ilevkivskyi]

If the function itself has no annotations then yes, it would make sense to not require annotations for locals.