update for guest demotion and sysadmin edits (#23920)

* update for guest demotion and sysadmin edits

* update unit test

* update unit test

* use existing disabled flag

* remove commented line

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/storetest/user_store.go

@@ -5699,7 +5699,7 @@ func testUserStoreDemoteUserToGuest(t *testing.T, ss store.Store) {
 
 		updatedUser, err := ss.User().DemoteUserToGuest(user.Id)
 		require.NoError(t, err)
-		require.Equal(t, "system_guest custom_role", updatedUser.Roles)
+		require.Equal(t, "system_guest", updatedUser.Roles)
 
 		updatedTeamMember, nErr := ss.Team().GetMember(context.Background(), teamId, user.Id)
 		require.NoError(t, nErr)