Flapping exemplars test failure

[tsloughter]

Saw this fail on OTP-23 in CI:

 %%% otel_metrics_SUITE ==> trace_based_exemplars: FAILED
%%% otel_metrics_SUITE ==> {{badmatch,[]},
 [{otel_metrics_SUITE,trace_based_exemplars,1,
                      [{file,"/home/runner/work/opentelemetry-erlang/opentelemetry-erlang/apps/opentelemetry_experimental/test/otel_metrics_SUITE.erl"},
                       {line,2228}]},
  {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1784}]},
  {test_server,run_test_case_eval1,6,[{file,"test_server.erl"},{line,1293}]},
  {test_server,run_test_case_eval,9,[{file,"test_server.erl"},{line,1225}]}]}