Add ref test for linking func arg default value (#140)

Author: felix-hilden

tests/extension/ref/ref_assign_targets.txt

@@ -1,24 +1,18 @@
 test_project
 bar
-Foo
 target
 bar
 target
-arg
-Foo
 # split
 # split
 Test project
 ============
 
 .. code:: python
 
-   from test_project import bar, Foo
+   from test_project import bar
 
    target = bar()
    target
 
-   def f(arg: Foo):
-       pass
-
 .. automodule:: test_project

tests/extension/ref/ref_func_args.txt

@@ -0,0 +1,18 @@
+test_project
+Foo
+arg
+Foo
+Foo
+# split
+# split
+Test project
+============
+
+.. code:: python
+
+   from test_project import Foo
+
+   def f(arg: Foo = Foo()):
+       pass
+
+.. automodule:: test_project