chore: filter DeprecationWarning

[waketzheng]

When running make test_postgres_asyncpg in local machine, the following warnings raised:

============================================== warnings summary ==============================================
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
  /Users/mac10.12/github/tortoise-orm/tortoise/fields/data.py:79: DeprecationWarning: `pk` is deprecated, please use `primary_key` instead
    super().__init__(primary_key=primary_key, **kwargs)

tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
tortoise/fields/data.py:79
  /Users/mac10.12/github/tortoise-orm/tortoise/fields/data.py:79: DeprecationWarning: `index` is deprecated, please use `db_index` instead
    super().__init__(primary_key=primary_key, **kwargs)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
1103 passed, 85 skipped, 3 xfailed, 16 warnings in 78.73s (0:01:18)

It is caused by this line initializer(["tests.testmodels"], db_url=db_url) in conftest.py as the there is a OldStyleModel in tests/testmodels.py

These warnings do not make any sense, it is better to ignore it.