lint: ruff format + one auto-fix so the push self-test is green again

`scripts/lint.sh --fix` from the pinned lint devshell: 90 Python files
reformatted (ruff format, mechanical) and one C420 (dict comprehension →
dict.fromkeys) in tests/unit/test_f211_sso_skip.py. The push self-test had
been failing at the lint stage since build 1313 (2026-08-31) on exactly
these files; nothing else changed.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FqkQq3CDmFWcQ7u1LzoyRz

tests/matrix-synapse/custom/test_register_and_message.py

@@ -127,8 +127,7 @@ def _admin_register(domain: str, secret: str, username: str, password: str, admi
         if r["status"] == 200:
             if attempt > 1:
                 print(
-                    f"  [register] {username}: succeeded on attempt {attempt} "
-                    f"(synapse recovered)",
+                    f"  [register] {username}: succeeded on attempt {attempt} (synapse recovered)",
                     flush=True,
                 )
             return r["body"] or {}
@@ -177,9 +176,9 @@ def test_register_two_users_send_receive_message(live_app):
     create + invite + join a room; send and read a message."""
     domain = live_app
     secret = _registration_secret(domain)
-    assert (
-        secret and len(secret) >= 16
-    ), f"registration shared secret missing/short: len={len(secret) if secret else 0}"
+    assert secret and len(secret) >= 16, (
+        f"registration shared secret missing/short: len={len(secret) if secret else 0}"
+    )
 
     suffix = uuid.uuid4().hex[:8]
     user_a = f"alice{suffix}"