test_dln.rb: fix path separator on MinGW
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60056 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_dln.rb: fix path separator on MinGW
RbConfig::CONFIG["PATH_SEPARATOR"] is : which is a separator on
msys2 shell building ruby. Use File::PATH_SEPARATOR ; on test.
[Bug #13642] [ruby-core:81623]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60056 b2dd03c8-39d4-4d8f-98ff-823fe69b080e