Use a ManualResetEvent in TestSubFileSystem.TestWatcherCaseSensitive

A bit friendlier for CI runners

Author: Metapyziks

src/Zio.Tests/FileSystems/TestSubFileSystem.cs

@@ -93,22 +93,22 @@ public void TestWatcherCaseSensitive(string physicalDir, string subDir, string f
 
         var subFs = new SubFileSystem(physicalFs, subDir);
         var watcher = subFs.Watch("/");
+        var waitHandle = new ManualResetEvent(false);
 
-        var gotChange = false;
         watcher.Created += (sender, args) =>
         {
             if (args.FullPath == filePath)
             {
-                gotChange = true;
+                waitHandle.Set();
             }
         };
 
         watcher.IncludeSubdirectories = true;
         watcher.EnableRaisingEvents = true;
 
         physicalFs.WriteAllText($"{physicalDir}{filePath}", "test");
-        Thread.Sleep(100);
-        Assert.True(gotChange);
+
+        Assert.True(waitHandle.WaitOne(100));
     }
 
     [SkippableFact]