Increase iteration count in the FinalizeTest (#62924)

Iteration count was dropped to a smaller number in dotnet/corert#2867. Looks like it's not enough because we see this test fail in the CI.

Author: MichalStrehovsky

src/tests/nativeaot/SmokeTests/BasicThreading/BasicThreading.cs

@@ -45,7 +45,7 @@ public class Dummy
     public static int Run()
     {
         int iterationCount = 0;
-        while (!visited && iterationCount++ < 10000)
+        while (!visited && iterationCount++ < 1000000)
         {
             GC.KeepAlive(new Dummy());
             GC.Collect();