fix: SaveScreenshotAsyncのコードを修正

Promete/Windowing/GLDesktop/OpenGLDesktopWindow.cs

@@ -190,7 +190,7 @@ public Texture2D TakeScreenshot()
 		public async Task SaveScreenshotAsync(string path, CancellationToken ct = default)
 		{
 			var img = TakeScreenshotAsImage();
-			await img.SaveAsPngAsync("path", ct);
+			await img.SaveAsPngAsync(path, ct);
 		}
 
 		public void Run()