Unable to create Model with custom PrimaryKey

Describe the bug
when creating a model, defining an attribute to be (pk=True) causes tortoise to throw the below error
tortoise.exceptions.ConfigurationError: Can't create model Post with two primary keys, only single primary key is supported
It seems to work fine if I explicitly define id as not being the PK
id=fields.SmallIntField(pk=False,required=False)
To Reproduce
Steps to reproduce the behavior, preferably a small code snippet.
Create a new model with a custom field as the primary key, but Do not explicitly define id:

class Post(BaseModel): id=fields.SmallIntField(pk=False,required=False) PostID = fields.SmallIntField(pk=True,unique=True) RawPost= fields.CharField(max_length=1600) Timestamp=fields.DatetimeField() Channel = fields.CharField(max_length=100) def __str__(self) -> str: return super(self.PostID).__str__()

Expected behavior
A clear and concise description of what you expected to happen.
Tortoise being smart enough to notice I'm defining a custom PK, without having to explicitly define id
Additional context
Add any other context about the problem here.
The Docs do not mention requiring to explicitly define id's pk as false.

Start by running the model definition in the issue, comparing the failing custom-primary-key case with the version that explicitly sets id=fields.SmallIntField(pk=False, required=False). Trace the model-field configuration that raises the two-primary-keys error; done means a custom primary key works without explicitly disabling the implicit id, with regression coverage for both cases.