Fix coverage test failure

Was failing with

    tests/test_ast.py:71: in <module>
        @parametrize_nodes()
    tests/test_ast.py:60: in parametrize_nodes
        nodes = [_instantiate_node(node_type) for node_type in node_types]
    tests/test_ast.py:55: in _instantiate_node
        return node_type(*([""] * len(node_type._fields)))
    E   TypeError: NodeList.__init__() missing 1 required positional argument: 'body'

coverage package adds a coverage.parser.NodeList subclass. See
nedbat/coveragepy@0accb68

tests/test_ast.py

@@ -30,6 +30,10 @@
 def _nodes_types(
     node_type: type[ast.AST] = ast.AST,
 ) -> Iterable[type[ast.AST]]:
+    # coverage package adds a coverage.parser.NodeList subclass
+    if node_type.__module__ != "ast":
+        return
+
     # Skip deprecated AST nodes.
     if issubclass(node_type, _deprecated_node_types):
         return