Use manual window startup location in macOS tests.

Seems to cause less flaky tests; `mainWindow.Click()` clicks the main window in the middle, where the secondary window is shown, so don't go out of our way to put the secondary window in front of where we're clicking.

tests/Avalonia.IntegrationTests.Appium/WindowTests_MacOS.cs

@@ -45,7 +45,7 @@ namespace Avalonia.IntegrationTests.Appium
         {
             var mainWindow = _session.FindElementByAccessibilityId("MainWindow");
 
-            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.CenterOwner))
+            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.Manual))
             {
                 mainWindow.Click();
 
@@ -63,7 +63,7 @@ namespace Avalonia.IntegrationTests.Appium
         {
             var mainWindow = FindWindow(_session, "MainWindow");
 
-            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.CenterOwner))
+            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.Manual))
             {
                 new Actions(_session)
                     .MoveToElement(mainWindow, 100, 1)
@@ -96,7 +96,7 @@ namespace Avalonia.IntegrationTests.Appium
 
             try
             {
-                using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.CenterOwner))
+                using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.Manual))
                 {
                     var windows = _session.FindElements(By.XPath("XCUIElementTypeWindow"));
                     var mainWindowIndex = GetWindowOrder(windows, "MainWindow");
@@ -119,7 +119,7 @@ namespace Avalonia.IntegrationTests.Appium
         {
             var mainWindow = _session.FindElementByAccessibilityId("MainWindow");
 
-            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Owned, WindowStartupLocation.CenterOwner))
+            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Owned, WindowStartupLocation.Manual))
             {
                 mainWindow.Click();
 
@@ -137,7 +137,7 @@ namespace Avalonia.IntegrationTests.Appium
         {
             var mainWindow = _session.FindElementByAccessibilityId("MainWindow");
 
-            using (OpenWindow(new PixelSize(1400, 100), ShowWindowMode.NonOwned, WindowStartupLocation.CenterOwner))
+            using (OpenWindow(new PixelSize(1400, 100), ShowWindowMode.NonOwned, WindowStartupLocation.Manual))
             {
                 mainWindow.Click();