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/mailu/custom/test_mail_flow.py

@@ -43,7 +43,7 @@ def test_send_and_receive_mail(live_app):
     deadline = time.time() + 150
     while time.time() < deadline:
         for box in ("INBOX", "Junk"):
-            query = f"doveadm search -u '{email_addr}' mailbox {box} " f"header subject '{marker}'"
+            query = f"doveadm search -u '{email_addr}' mailbox {box} header subject '{marker}'"
             out = lifecycle.exec_in_app(live_app, ["sh", "-c", query], service="imap")
             if out.strip():  # a non-empty result = "<mailbox-guid> <uid>" → message stored
                 return