Fix multiple instances of a game being allowed to start concurrently

[peppy]

Regressed with #6442. Closes ppy/osu#31072.

Was not visible in test coverage because as per the inline comment, this is an exceptional case where two different processes bind.

I'm not sure how to add test coverage for this, but I have tested manually on both windows and macOS.

Can test using this:

diff --git a/SampleGame.Desktop/Program.cs b/SampleGame.Desktop/Program.cs
index 4756edbaa..ae5075535 100644
--- a/SampleGame.Desktop/Program.cs
+++ b/SampleGame.Desktop/Program.cs
@@ -12,9 +12,17 @@ public static class Program
         [STAThread]
         public static void Main(string[] args)
         {
-            using (GameHost host = Host.GetSuitableDesktopHost(@"sample-game"))
+            using (GameHost host = Host.GetSuitableDesktopHost(@"sample-game", new HostOptions
+                   {
+                       IPCPipeName = "wang"
+                   }))
             using (Game game = new SampleGameGame())
+            {
+                if (host.IsPrimaryInstance)
+                    return;
+
                 host.Run(game);
+            }
         }
     }
 }