fix #1462, add field_type for TimeDeltaField

[yinkh]

Description

fix https://github.com/tortoise/tortoise-orm/issues/1462

Motivation and Context

use pydantic_model_creator with fields.TimeDeltaField in 0.19.3 will get error

pydantic.error_wrappers.ValidationError: 1 validation error for DemoSchema
usage_time
  value is not None (type=type_error.not_none)

How Has This Been Tested?

https://github.com/tortoise/tortoise-orm/assets/8170059/fa70fa98-0ebe-4c97-80da-2537ce0ac724

python3.9 pydantic 1.10.12 tortoise-orm 0.19.3

tortoise/fields/data.py:501

Checklist:

• [yes ] My code follows the code style of this project.
• [no] My change requires a change to the documentation.
• [no] I have updated the documentation accordingly.
• [no] I have added the changelog accordingly.
• [yes ] I have read the CONTRIBUTING document.
• [no ] I have added tests to cover my changes.
• [no ] All new and existing tests passed.

[abondar]

Please add testcase reproducing issue to tests/contrib/test_pydantic.py

[DavideGalilei]

Bump. Having the same issue, the PR solution fixed it.