Fix Breaking Change Detection on Inheritence

[Louis-Dupont]

Context

Let's imagine we change the code

FROM

class MyClass:
    def method(self): pass

TO

class MyNewClass:
    def method(self): pass

class MyClass(MyNewClass): pass

This is NOT a breaking change, because MyClass inherits from MyNewClass which still includes method.

Issue: current class signature extractor (implemented as part of the breaking change detection) currently misses this and will raise that the new MyClass does not include method.

[BloodAxe]

LGTM

[BloodAxe]

LGTM