test: add nested functions

Author: nohehf

languages/tree-sitter-stack-graphs-python/test/nested_functions.py

@@ -0,0 +1,11 @@
+def outer(a):
+    def inner(b, c):
+        pass
+
+    inner(1)
+    # ^ defined: 2
+
+
+class A:
+    def method(a):
+        pass