Fix a lot of test related typing issues

test/test_inference/test_mixed.py

@@ -56,10 +56,10 @@ def test_generics_methods(code, expected, class_findable):
     class Reader(Generic[T]):
         @classmethod
         def read(cls) -> T:
-            return cls()
+            return cls()  # type: ignore[return-value]
 
         def method(self) -> T:
-            return 1
+            return 1  # type: ignore[return-value]
 
     class Foo(Reader[str]):
         def transform(self) -> int:
@@ -94,7 +94,7 @@ def test_signature():
         pass
 
     from inspect import Signature, Parameter
-    some_signature.__signature__ = Signature([
+    some_signature.__signature__ = Signature([  # type: ignore[attr-defined]
         Parameter('bar', kind=Parameter.KEYWORD_ONLY, default=1)
     ])
 
@@ -105,7 +105,7 @@ def test_signature():
 def test_compiled_signature_annotation_string():
     import typing
 
-    def func(x: typing.Type, y: typing.Union[typing.Type, int]):
+    def func(x: typing.Type, y: typing.Union[typing.Type, int]):  # type: ignore[type-arg]
         pass
     func.__name__ = 'not_func'