test_etc.rb: fix for non unique GID
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36833 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_etc.rb: fix for non unique GID
No unixen systems guarantee that GID is unique. Etc.getgrgid would
not return the first entry in the order of Etc.group for shared GID.
[ruby-core:47312] [Bug #6935]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36833 b2dd03c8-39d4-4d8f-98ff-823fe69b080e