graphics/py-ueberzug: Fix packaging with Python 3.8+

* Apply the same fix as in 9cb5898 by
  stripping libraries by wildcard paths.

* Also use PYTHONPREFIX_SITELIBDIR instead PYTHON_SITELIBDIR to make
  the port PREFIX safe while I'm here.

PR:		253815
Approved by:	python (with hat)

graphics/py-ueberzug/Makefile

@@ -28,7 +28,7 @@ PORTEXAMPLES=	fzfimg.sh mastodon.sh
 OPTIONS_DEFINE=	EXAMPLES
 
 post-install:
-	${STRIP_CMD} ${STAGEDIR}${PYTHON_SITELIBDIR}/Xshm.so
+	${STRIP_CMD} ${STAGEDIR}${PYTHONPREFIX_SITELIBDIR}/Xshm*.so
 
 post-install-EXAMPLES-on:
 	${MKDIR} ${STAGEDIR}${EXAMPLESDIR}