test(session-storage): accept the cached kwarg in cotenant_sids forge-safe mocks

[RohanK6]

Problem / Motivation

main CI is red on Backend Tests shard 3 (3.10, 3.12, Windows). Two forge-safe test mocks in test/test_session_storage.py (TestCotenantRefusalTextIsForgeSafe, lines ~2504/2524) monkeypatch cotenant_sids with a no-argument lambda, but production now calls cotenant_sids(cached=cached) (the function is def cotenant_sids(*, cached: bool = False)). The code under test therefore raises TypeError: <lambda>() got an unexpected keyword argument 'cached'.

Why it matters

This is a main-side breakage, not specific to one PR: main's own CI fails this job (e.g. run 33159160070 on 16239989d, and the latest on 5c925e4e3), so every PR rebased onto current main inherits a red shard-3 and cannot reach green. A one-PR-blocks-none fix unblocks the whole queue.

What changed (motivation → approach → change)

• Symptom: TypeError on the cached kwarg in test_move_to_trash_refusal_error_escapes_the_name (and the sibling reclaim_block_reason test), failing shard 3 on all platforms.
• Root cause: a PR that added the keyword-only cached parameter to cotenant_sids updated the real call sites but missed these two mock lambdas.
• Change: update both mocks to accept the keyword-only arg, mirroring the real signature: lambda *, cached=False: (frozenset(), self._REFUSALS). Two lines (plus black line-wrapping). No production code touched.

Tests

test/test_session_storage.py::TestCotenantRefusalTextIsForgeSafe passes 2/2 locally with the fix (previously errored on both). black --check clean. No other no-arg cotenant_sids mock lambdas remain in the file.

Related Issues

Fixes #6523

Checklist

• At most two commits (one), with a Conventional Commits title
• Existing tests pass and new tests added for new functionality — N/A (repairs an existing test's mock; no behavior change)
• Self-review completed; code follows project style guidelines
• Documentation updated (if applicable) — N/A
• No secrets, credentials, or internal references in the diff

[RohanK6]

Superseded by #6517 (main commit e48ea42), which fixed the same cotenant_sids forge-safe mock breakage on main. main CI is green again; closing as redundant.