service/http_get_isolate_group_rpc_test fails on dartk release bots

[aam]

Newly added service/http_get_isolate_group_rpc_test fails on
https://ci.chromium.org/p/dart/builders/ci.sandbox/vm-kernel-linux-release-simarm/7213,
https://ci.chromium.org/p/dart/builders/ci.sandbox/vm-kernel-linux-release-ia32/4738,
https://ci.chromium.org/p/dart/builders/ci.sandbox/vm-kernel-win-release-x64/7862