www/py-django30: Set to expire

* Set the EXPIRATION_DATE to make it clearer that consumers need to
  switch to another Django version as soon as possible.

Reported by:	rene
Approved by:	python (with hat)

www/py-django30/Makefile

@@ -17,6 +17,7 @@ LICENSE=	BSD3CLAUSE
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 DEPRECATED=	Has expired: Extended support has expired on April 6th, 2021. Use www/py-django31 or www/py-django32 instead
+EXPIRATION_DATE=	2021-05-16
 
 RUN_DEPENDS=	${PYTHON_PKGNAMEPREFIX}pytz>0:devel/py-pytz@${PY_FLAVOR} \
 		${PYTHON_PKGNAMEPREFIX}asgiref>0:www/py-asgiref@${PY_FLAVOR} \