[gardening] Mark samples/ffi/http/test_http_test extra slow.

Fixes #61583
TEST=ci

Change-Id: Ib9c484787e0665cc60bf63c693b5e7458b211eea
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/454401
Reviewed-by: Brian Quinlan <[email protected]>
Commit-Queue: Alexander Aprelev <[email protected]>

Author: aam

samples/samples.status

@@ -2,7 +2,7 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-ffi/http/test/http_test: Pass, Slow # https://dartbug.com/61583
+ffi/http/test/http_test: Pass, ExtraSlow # https://dartbug.com/61583
 
 [ $sanitizer == asan ]
 ffi/samples_test: SkipByDesign # FFI skips, see ffi.status