Fix countdown event wait (#567)

Fix countdown event wait

Author: MarcoRossignoli

src/coverlet.collector/Utilities/CountDownEvent.cs

@@ -31,13 +31,10 @@ public void Signal()
 
         public void Wait()
         {
-            // We wait on another thread to avoid to block forever
-            // We could use Task/Task.Delay timeout trick but this api and collector are sync so to
-            // avoid too much GetAwaiter()/GetResult() I prefer keep code simple.
-            // This thread is created only one time where we pass coverage files 
-            var waitOnThread = new Thread(() => _countDownEvent.Wait());
-            waitOnThread.Start();
-            waitOnThread.Join(_waitTimeout);
+            if (!_countDownEvent.Wait(_waitTimeout))
+            {
+                throw new TimeoutException($"CollectorCountdownEvent timeout after {_waitTimeout}");
+            }
         }
     }
 }