test: annotate the broker helper for faststream 0.7.6

[lesnik512]

main went red without a commit. faststream 0.7.6 was published at 2026-09-20T09:27:20Z; the last
green run on main was 08:42Z. uv.lock is gitignored, so CI resolves dependencies fresh on every
run and picked the new release up immediately.

BrokerUsecase gained a third type parameter, defaulting to BrokerConfig. RedisBroker binds its
own config type, so it is no longer assignable to the two-parameter spelling and ty reports 15
invalid-argument-type diagnostics against the single helper in
tests/test_faststream_bootstrap.py:

Expected `BrokerUsecase[Any, Any, BrokerConfig] | None`, found `RedisBroker`

Spelling the third parameter as typing.Any fixes it. Dropping the parameters entirely does not -
the default still resolves to BrokerConfig and all 15 diagnostics remain.

Verified against both versions in a clean worktree, since CI may resolve either:

faststream	ty check	tests/test_faststream_bootstrap.py
0.7.4	clean	22 passed
0.7.6	clean	22 passed

Test-only; no production code and no runtime behaviour changes.

Not done here, worth deciding separately: uv.lock being gitignored is what turns any upstream
release into an immediate red main. Tracking it would make these arrive as a deliberate bump
instead.