Enums not quoted (bug of pypika-torotise)

[waketzheng]

Describe the bug
Reported here: tortoise/pypika-tortoise#7

To Reproduce

from tortoise import Model, fields, run_async
from tortoise.contrib.test import init_memory_sqlite
from tortoise.fields.base import StrEnum


class MyModel(Model):
    id = fields.IntField(pk=True)
    name = fields.TextField()


class MyEnum(StrEnum):
    A = "a"


@init_memory_sqlite
async def do():
    await MyModel.create(name="a")
    qs = MyModel.filter(name=MyEnum.A)
    qs._make_query()
    print(qs.query)
    # expected   SELECT "id","name" FROM "mymodel" WHERE "name"='a'
    # actual     SELECT "id","name" FROM "mymodel" WHERE "name"=a
    print(await MyModel.filter(name=MyEnum.A).exists())
    # expected True
    # actual raises tortoise.exceptions.OperationalError: no such column: a


run_async(do())

Expected behavior
Support filter by enum

Additional context
Will be fixed after this PR(tortoise/pypika-tortoise#10) merged.