Fix nested assignments in Python.

Author: Bastiaan Marinus van de Weerd

languages/tree-sitter-stack-graphs-python/src/stack-graphs.tsg

@@ -158,6 +158,7 @@ attribute node_symbol = node            => symbol = (source-text node), source_n
   (generator_expression)
   (ellipsis)
   (list_splat)
+  (assignment)
 
   ; expression list
   (expression_list)

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

@@ -0,0 +1,11 @@
+x = 42
+
+print(x)
+#     ^ defined: 1
+
+y = z = 1337
+
+print(x, y, z)
+#     ^ defined: 1
+#        ^ defined: 6
+#           ^ defined: 6