devel/py-unicodedata2: limit supported python versions

./unicodedata2/py3/unicodedata.c:19:10: fatal error: 'ucnhash.h' file not found
#include "ucnhash.h"
         ^~~~~~~~~~~

Approved by:	portmgr blanket

devel/py-unicodedata2/Makefile

@@ -13,7 +13,7 @@ COMMENT=	Unicodedata backport and updates
 LICENSE=	APACHE20
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
-USES=		python:3.6+
+USES=		python:3.6-3.9
 USE_PYTHON=	autoplist concurrent distutils
 
 post-install: