devel/py-pydantic-settings: Fix BUILD_DEPENDS usage: it should depend on the package, not the executable

from pyproject.toml:
[build-system]
requires = ['hatchling']

Reference: https://github.com/pydantic/pydantic-settings/blob/v2.6.0/pyproject.toml#L1-L2
Approved by: portmgr (blanket)
With hat: python