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/mattermost-lts/custom/test_multiuser_message.py

@@ -105,6 +105,6 @@ def test_second_user_reads_first_users_message(live_app):
 
     # 5) user_b sees user_a's marker (cross-user delivery, not a self read-back)
     messages = [p.get("message") for p in (posts.get("posts") or {}).values()]
-    assert (
-        marker in messages
-    ), f"user_b did not see user_a's message {marker!r} in the channel; saw {messages!r}"
+    assert marker in messages, (
+        f"user_b did not see user_a's message {marker!r} in the channel; saw {messages!r}"
+    )