devel/rubygem-stringio: Update to 3.0.6

Changes:	https://github.com/ruby/stringio/releases
		https://github.com/ruby/stringio/blob/master/NEWS.md

devel/rubygem-stringio/Makefile

 PORTNAME=	stringio
-PORTVERSION=	3.0.5
+PORTVERSION=	3.0.6
 CATEGORIES=	devel rubygems
 MASTER_SITES=	RG
 

devel/rubygem-stringio/distinfo

-TIMESTAMP = 1677771639
-SHA256 (rubygem/stringio-3.0.5.gem) = 3aae21623264ceff12eee4124a50940b21e3ee9b7469e4e5c0c0b5e1f71680aa
-SIZE (rubygem/stringio-3.0.5.gem) = 16384
+TIMESTAMP = 1681843938
+SHA256 (rubygem/stringio-3.0.6.gem) = fbf8bb626f3f835d32922199c42e0e962499fd1d355044445793100469368483
+SIZE (rubygem/stringio-3.0.6.gem) = 16384