Fix deadlock for Sanic apps with generate_schema=True and > 1 workers

[Pirulax]

Description/Motivation and Context

Fixes deadlock caused by multiple workers trying to initialize the schema at the same time.
In my case this deadlock was caught by asyncpg.
I did try making a minimum repro sample, but failed, and honestly, don't have the time to fiddle with it.
I can't post my app, as it's private.

How Has This Been Tested?

I ran it in my own app where the deadlock previously occurred, now it doesn't and the schema is created as expected.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[abondar]

Hi!

Please run make lint to see lint errors

[Pirulax]

Hello,
Not sure if there are docs of this somewhere, but on Windows both make lint and make style fails out of the box.
I had to manually install black and isort using pipx.

[coveralls]

Pull Request Test Coverage Report for Build 10393052714

Details

• 0 of 9 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.07%) to 89.021%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/contrib/sanic/init.py	0	9	0.0%

Totals
Change from base Build 10244831838:	-0.07%
Covered Lines:	5960
Relevant Lines:	6580

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💛 - Coveralls