Fix flake8 violation under tests/

tests/test_util_nodes.py

@@ -87,7 +87,6 @@ def test_extract_messages():
         nodes.rubric, 1,
     )
 
-
     text = dedent(
         """
         | spam
@@ -100,7 +99,6 @@ def test_extract_messages():
         nodes.line, 2,
     )
 
-
     text = dedent(
         """
         section
@@ -118,7 +116,6 @@ def test_extract_messages():
         nodes.line, 2,
     )
 
-
     text = dedent(
         """
         * | **Title 1**