test(patreon): fix _BoomSession stub for the B5 headers kwarg

test_one_failure_isolated's _BoomSession overrode get() without the headers
kwarg _fetch_to_file now passes (B5 Range resume), so the call TypeError'd and
both items errored. Add headers=None to match the base fake.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_patreon_downloader.py

@@ -289,7 +289,7 @@ def test_video_permanent_failure_fails_fast(tmp_path, monkeypatch):
 
 def test_one_failure_isolated(tmp_path):
     class _BoomSession(_FakeSession):
-        def get(self, url, stream=False, timeout=None):
+        def get(self, url, stream=False, timeout=None, headers=None):
             self.calls.append(url)
             if "bad" in url:
                 raise RuntimeError("network boom")