textproc/py-pallets-sphinx-themes: Fix RUN_DEPENDS

• Bump PORTREVISION for dependency change

from setup.py:

install_requires = [
    "importlib-metadata; python_version < '3.8'",
    "packaging",
    "Sphinx",
]

Approved by: portmgr (blanket)
With hat: python
Reference: https://github.com/pallets/pallets-sphinx-themes/blob/2.0.2/setup.py#L5-L9