style: repo-wide lint pass — make the lint gate green again

Push builds have been RED on the lint step since ~build 209 from accumulated
formatting drift. This is the mechanical cleanup: ruff format + ruff --fix
(UP038 isinstance unions, SIM105 contextlib.suppress, UP031 f-strings, SIM115
tempfile context manager), shfmt -i 2 -ci, nixpkgs-fmt/statix/deadnix (merged
attrsets, dropped unused lib args), yamllint, and shell quoting fixes in
tests/lasuite-docs/setup_custom_tests.sh. No behaviour changes intended;
lint: PASS, unit tests: 138 passed.

tests/mattermost-lts/test_install.py

@@ -15,6 +15,4 @@ def test_serving_and_api(live_app, meta):
     generic.assert_serving(live_app, meta)
     # ... then the recipe-specific assertion: the mattermost REST liveness endpoint answers 200.
     status = lifecycle.http_get(live_app, "/api/v4/system/ping")
-    assert status == 200, (
-        f"expected 200 from {live_app}/api/v4/system/ping, got {status}"
-    )
+    assert status == 200, f"expected 200 from {live_app}/api/v4/system/ping, got {status}"