fix: migrate broken team authorize access mode (#39579)

* fix:  #39571
* ref: https://github.com/go-gitea/gitea/pull/38938#pullrequestreview-4945228548
* fix the bug in `assignTeamPermissionUnits` which can result in wrong team access

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/org/team.go

@@ -167,6 +167,7 @@ func assignTeamPermissionUnits(team *organization.Team, permission string, units
 	oldAccessMode := team.AccessMode
 	oldUnitPerms := team.GetUnitsMap()
 	if len(unitsMap) > 0 {
+		team.AccessMode = perm.AccessModeNone
 		team.Units = make([]*organization.TeamUnit, 0, len(unitsMap))
 		for unitKey, p := range unitsMap {
 			unitType, unitPerm := unit_model.TypeFromKey(unitKey), perm.ParseAccessMode(p)