mark barback test "too_many_open_files_test" as flaky

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 520631cc5cc5c9567cfa6b4a976bfa2cb6e8aa30..bba14b725b31da5bfe8bf073bde455bc2c1c4dfe 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -219,10 +219,9 @@ unittest/test/*_minified_test: Skip # DO NOT COPY THIS UNLESS YOU WORK ON DART2J
 *: Skip  # Issue 13624
 
 [ $arch == simarm || $arch == simmips ]
-barback/test/too_many_open_files_test: Pass, Slow
+barback/test/too_many_open_files_test: Pass, Slow, Fail # 14220
 third_party/html5lib/test/tokenizer_test: Pass, Slow
 watcher/test/no_subscription_test: Pass, Fail  # Issue 13705.
-barback/test/too_many_open_files_test: Pass, Slow
 
 # Skip serialization test that explicitly has no library declaration in the
 # test on Dartium, which requires all tests to have a library.