github: make user/pass the default auth mode over TTY

Make username/password authentication the default mode when presented
with the options over the TTY. This is because we still don't have a
whitelisted OAuth application and any OAuth tokens will have
restrictions when used for org-owned repos.

Author: mjcheetham

src/shared/GitHub/GitHubAuthentication.cs

@@ -123,8 +123,8 @@ public async Task<AuthenticationPromptResult> GetAuthenticationAsync(Uri targetU
                         var menuTitle = $"Select an authentication method for '{targetUri}'";
                         var menu = new TerminalMenu(Context.Terminal, menuTitle)
                         {
-                            new TerminalMenuItem(1, "Web browser", true),
-                            new TerminalMenuItem(2, "Username/password")
+                            new TerminalMenuItem(1, "Web browser"),
+                            new TerminalMenuItem(2, "Username/password", true)
                         };
 
                         int option = menu.Show();