test_io.rb: increase timeout for RubyCI

to stabilize AIX powerpc CI

https://rubyci.org/logs/rubyci.s3.amazonaws.com/aix71_ppc/ruby-trunk/log/20181227T113302Z.fail.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66618 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -3361,7 +3361,7 @@ __END__
       }
 
       IO.select(tempfiles)
-    }, bug8080, timeout: 50
+    }, bug8080, timeout: 100
   end if defined?(Process::RLIMIT_NOFILE)
 
   def test_read_32bit_boundary