test_io.rb: ignore not-implemented fadvice

* test/ruby/test_io.rb (test_advise_pipe): ignore not-implemented
  fadvice(2) when it is present but not implemented, as IO#advice
  does nothing and raises no exceptions.  [Feature #11806]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53139 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -3005,8 +3005,12 @@ End
     # we don't know if other platforms have a real posix_fadvise()
     with_pipe do |r,w|
       # Linux 2.6.15 and earlier returned EINVAL instead of ESPIPE
-      assert_raise(Errno::ESPIPE, Errno::EINVAL) { r.advise(:willneed) }
-      assert_raise(Errno::ESPIPE, Errno::EINVAL) { w.advise(:willneed) }
+      assert_raise(Errno::ESPIPE, Errno::EINVAL) {
+        r.advise(:willneed) or skip "fadvice(2) is not implemented"
+      }
+      assert_raise(Errno::ESPIPE, Errno::EINVAL) {
+        w.advise(:willneed) or skip "fadvice(2) is not implemented"
+      }
     end
   end if /linux/ =~ RUBY_PLATFORM