[flutter_tools] pin frontend_server_client because upgrading from 3.2.0 -> 4.0.0 regresses test #146164
Description
Example failing build: https://ci.chromium.org/p/flutter/builders/try/Windows%20tool_integration_tests_2_6/26698?
From attempted roll: #145959
Upstream tracking issue: dart-lang/webdev#2377