textproc/py-ocrmypdf: Update to 15.4.4

• Note: The 16.x series has already been released recently, but here Python 3.10 is required as a minimum.
  
  Thus, use the last release of the 15.x series until the default Python version in the FreeBSD ports tree has been changed to 3.10 or later.

Changelog since 15.4.0:

https://github.com/ocrmypdf/OCRmyPDF/blob/v15.4.4/docs/release_notes.rst