Fix BlackSheep cross-task database access

[Sanjays2402]

Description

Enable the global context fallback when the BlackSheep integration initializes Tortoise.

Motivation and Context

BlackSheep startup and request handlers run in separate asyncio tasks. Without the fallback, every request-side database query raises No TortoiseContext is currently active. Fixes #2244.

How Has This Been Tested?

The regression test fails without the flag and passes with it. A BlackSheep lifecycle probe also initialized the ORM in one task and successfully queried SQLite from another.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation. (Not required.)
• I have updated the documentation accordingly. (Not required.)
• I have added the changelog accordingly. (Not required.)
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed. (The focused test passed; the full suite was not run.)

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing Sanjays2402:fix/blacksheep-global-context (9d35ff7) with develop (8c12adc)}

[waketzheng]

Please fix lint issue.

[Sanjays2402]

The failing job was check — mypy, not ruff:

tests/contrib/test_blacksheep.py:24: error: Call to untyped function "start" in typed context  [no-untyped-call]
tests/contrib/test_blacksheep.py:33: error: Call to untyped function "stop" in typed context  [no-untyped-call]

disallow_untyped_calls = true applies to tests too (the tests.* override only relaxes check_untyped_defs/disallow_untyped_defs), and blacksheep's Application.start/stop are unannotated upstream. Added # type: ignore[no-untyped-call] on the two call sites, matching how tests elsewhere in the repo handle third-party typing gaps.

mypy tests/contrib/test_blacksheep.py and ruff format --check/ruff check are clean, and pytest tests/contrib/test_blacksheep.py is 1 passed. Pushed 9d35ff7.