textproc/py-ocrmypdf: Update to 13.7.0

There is already a new major release (= 14.x) out, but the build system
has been changed here, which therefore takes a little more time to
implement. So use the last release of the 13.x series for a while.

Changelog since 13.6.0:

https://github.com/ocrmypdf/OCRmyPDF/blob/v13.7.0/docs/release_notes.rst

MFH: 2022Q4