Add SET DEFAULT and NO ACTION to OnDeleteType

[anxkhn]

OnDeleteType, the Literal that types the public Field(ondelete=...)
parameter, only listed three of the five standard SQL referential actions:
CASCADE, SET NULL and RESTRICT. The remaining two, SET DEFAULT and
NO ACTION, are valid everywhere else in the stack: ondelete is passed
straight through to SQLAlchemy's ForeignKey(ondelete=...), which emits
ON DELETE <value> for any of them, and SQL defines exactly these five actions.

Because the literal omitted them, a type checker (mypy/pyright/ty) rejected a
perfectly valid schema, for example:

class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    team_id: int | None = Field(
        default=None, foreign_key="team.id", ondelete="NO ACTION"
    )

The only workarounds were casting to Any or dropping down to sa_column.
NO ACTION is the default referential action in PostgreSQL and most databases,
and SET DEFAULT pairs naturally with a column server_default, so both are
things people legitimately want to spell out.

This adds the two missing actions to OnDeleteType. There is no runtime change
(the value was always passed through unchanged); this only corrects the static
type. Reported in #1839.

Tests

Added a parametrized regression test over the two newly typed actions that
asserts both the resulting foreign key's ondelete and the generated
ON DELETE <action> DDL, mirroring the existing
test_foreign_key_ondelete_with_annotated.

[github-actions]

This was marked as potentially AI generated and will be closed now. If this is an error, please provide additional details, make sure to read the docs about contributing and AI.