[gardening] Mark service/async_generator_breakpoint_test/ as slow in release mode

This test uses --stacktrace-every= which will cause it to be slow. It
was marked only as slow in debug mode, which this CL extends to all
other modes as well.

This addresses timeout of service/async_generator_breakpoint_test.

TEST=service/async_generator_breakpoint_test

Change-Id: I7576d7c1a392ff75ee779278ceb79f9681b8157c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217005
Reviewed-by: Tess Strickland <sstrickl@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

runtime/observatory/tests/service/service.status

diff --git a/runtime/observatory/tests/service/service.status b/runtime/observatory/tests/service/service.status
index de8b15b..c7e818c 100644
--- a/runtime/observatory/tests/service/service.status
+++ b/runtime/observatory/tests/service/service.status
@@ -2,6 +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.
 # Flaky failures
+async_generator_breakpoint_test: Pass, Slow # Uses --stacktrace-every=...
 dds_log_history_size_gigantic_test: Pass, Slow # Involves processing lots of logs
 field_script_test: Pass, RuntimeError
 get_allocation_samples_test: Pass, RuntimeError # Inconsistent stack trace
@@ -22,10 +23,6 @@
 [ $compiler == dart2analyzer ]
 developer_extension_test: SkipByDesign
 
-# The _1 versions of this test can be slow due to stress testing flags.
-[ $mode == debug ]
-async_generator_breakpoint_test: Pass, Slow
-
 # Service protocol is not supported in product mode.
 [ $mode == product ]
 *: SkipByDesign