Methods on values returned by functions do not lead to correct output

[koebi]

Describe the bug
str.removeprefix() does not get discovered as needing 3.9 when used on the return type of a method, even if it's a string.

To Reproduce
Running vermin on

def foo() -> str:
    return "Foobar"

a = foo()
b = a.removeprefix("Foo")

returns

Minimum required versions: 3.0

Expected behavior
It should return 3.9.

Environment (please complete the following information):
vermin version 1.6.0