add missing blank line after class docstring in linkcheck test

Author: FazeelUsmani

tests/test_builders/test_build_linkcheck.py

@@ -1443,6 +1443,7 @@ def test_linkcheck_exclude_documents(app: SphinxTestApp) -> None:
 
 class CaseSensitiveHandler(BaseHTTPRequestHandler):
     """Handler that returns URLs with uppercase in the redirect location."""
+    
     protocol_version = 'HTTP/1.1'
 
     def do_HEAD(self):