new port: devel/py-decorator4

devel/py-decorator needs to be updated to 5.x, while some ports don't
support that in their latest releases, including:

• devel/py-pytest-relaxed
• multimedia/py-moviepy

Updated them to use this devel/py-decorator4 until they officially
support 5.x. No functional changes for these ports.

An expiry date has been set for this keeping-old-version port, so we
don't forget to delete it once nothing depends on it.

Approved by: lwhsu (mentor)