test(gcp consumer): stabilize flaky test
https://github.com/emqx/emqx/actions/runs/9614788348/job/26526973635?pr=13317#step:5:1463
```
%%% emqx_bridge_gcp_pubsub_consumer_SUITE ==> t_connection_down_before_starting: FAILED
%%% emqx_bridge_gcp_pubsub_consumer_SUITE ==> {{panic,
#{msg => "Unexpected result",
result =>
{run_stage_failed,error,
{assertMatch,
[{module,emqx_bridge_gcp_pubsub_consumer_SUITE},
{line,1451},
{expression,"health_check ( Config )"},
{pattern,"{ ok , connecting }"},
{value,{ok,disconnected}}]},
[{emqx_bridge_gcp_pubsub_consumer_SUITE,
'-t_connection_down_before_starting/1-fun-11-',4,
[{file,
"/emqx/apps/emqx_bridge_gcp_pubsub/test/emqx_bridge_gcp_pubsub_consumer_SUITE.erl"},
{line,1451}]},
{emqx_bridge_gcp_pubsub_consumer_SUITE,
t_connection_down_before_starting,1,
[{file,
"/emqx/apps/emqx_bridge_gcp_pubsub/test/emqx_bridge_gcp_pubsub_consumer_SUITE.erl"},
{line,1427}]}]}}},
[{emqx_bridge_gcp_pubsub_consumer_SUITE,t_connection_down_before_starting,1,
[{file,
"/emqx/apps/emqx_bridge_gcp_pubsub/test/emqx_bridge_gcp_pubsub_consumer_SUITE.erl"},
{line,1462}]},
{test_server,ts_tc,3,[{file,"test_server.erl"},{line,1793}]},
{test_server,run_test_case_eval1,6,[{file,"test_server.erl"},{line,1302}]},
{test_server,run_test_case_eval,9,[{file,"test_server.erl"},{line,1234}]}]}
```
c9ec5ac87b