test: Wait start task for SuccessfulRequestCausesDataToBeStoredAndDataSourceInitialized. (#200)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Waits for the `Start()` task to complete (with timeout) before
asserting `Initialized` in
`SuccessfulRequestCausesDataToBeStoredAndDataSourceInitialized`.
> 
> <sup>Written by [Cursor
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<!-- /CURSOR_SUMMARY -->

Author: kinyoklion

pkgs/sdk/server/test/Internal/DataSources/PollingDataSourceTest.cs

@@ -66,7 +66,8 @@ public void SuccessfulRequestCausesDataToBeStoredAndDataSourceInitialized()
 
                     var receivedData = _updateSink.Inits.ExpectValue();
                     AssertHelpers.DataSetsEqual(AllData, receivedData);
-
+                    
+                    initTask.Wait(TimeSpan.FromSeconds(1));
                     Assert.True(dataSource.Initialized);
 
                     Assert.True(initTask.IsCompleted);