[PLAT-11178] Update sampling probability test fixture (#368)

* test: 🧪 isolate flakey test scenario

* test: ✅ await sampling request before starting the span

* test: ✅ remove scenario isolation

test/react-native/features/persistent-state.feature

@@ -22,6 +22,7 @@ Scenario: Invalid sampling value is ignored on app launch
 Scenario: Expired sampling value is ignored on app launch
   Given I execute the command "set-expired-sampling-probability"
   When I run "SpanTriggeredByCommandScenario"
+  And I wait to receive a sampling request
   And I execute the command "start-span"
   Then I wait to receive 1 trace