Bump MonoTouch.Dialog and Touch.Unit.

New commits in migueldeicaza/MonoTouch.Dialog:

* migueldeicaza/MonoTouch.Dialog@f500f9a Bump to .NET 8.

Diff: https://github.com/migueldeicaza/MonoTouch.Dialog/compare/94359c74ef481ce7b5daa28b890f35a6e77d94c8..f500f9a48dbf856c693b255078e1507cf1e8edde

New commits in spouliot/Touch.Unit:

* xamarin/Touch.Unit@5739ade Bump to .NET 8.

Diff: https://github.com/spouliot/Touch.Unit/compare/8d80e1f10414ec85afa14c8c45a05334eb37c6dd..5739adefc261b7bfeb70ff718c7b2d97bdfa42ee

.gitmodules

@@ -13,15 +13,15 @@
 [submodule "external/Touch.Unit"]
     path = external/Touch.Unit
     url = ../../spouliot/Touch.Unit.git
-    branch = main
+    branch = net8.0
 [submodule "external/Xamarin.MacDev"]
     path = external/Xamarin.MacDev
     url = ../../xamarin/Xamarin.MacDev
     branch = main
 [submodule "external/MonoTouch.Dialog"]
     path = external/MonoTouch.Dialog
     url = ../../migueldeicaza/MonoTouch.Dialog
-    branch = dotnet
+    branch = net8.0
 [submodule "api-tools"]
     path = external/api-tools
     url = ../../rolfbjarne/api-tools