style: satisfy ruff-format on conftest.py (PER-15243)

The autouse throttle-reset fixture sits directly above a module-level `if`; ruff-format
(the pre-commit hook, distinct from ruff check) requires two blank lines there. Whitespace only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: dshoen619

horizon/tests/conftest.py

@@ -38,6 +38,7 @@ def _reset_operational_warn_throttle():
     _authentication.reset_operational_warn_throttle()
     yield
 
+
 if "stream_writer" in inspect.signature(_ClientResponse.__init__).parameters:
 
     class _StreamWriterCompatClientResponse(_ClientResponse):