Duplicate group assignation to a ticket

[btry]

Describe the bug
see last posts from #1042

See the errors bellow.

*** MySQL query error:
SQL: INSERT INTO glpi_groups_tickets (tickets_id, groups_id, type) VALUES ('15724', '9', '2')
Error: Duplicate entry '15724-2-9' for key 'unicity'
Backtrace :
inc/dbmysql.class.php:917
inc/commondbtm.class.php:537 DBmysql->insert()
inc/commondbtm.class.php:974 CommonDBTM->addToDB()
inc/commonitilobject.class.php:1558 CommonDBTM->add()
inc/ticket.class.php:2160 CommonITILObject->post_addItem()
inc/commondbtm.class.php:975 Ticket->post_addItem()
...ins/formcreator/inc/targetticket.class.php:1261 CommonDBTM->add()
plugins/formcreator/inc/form_answer.class.php:1030 PluginFormcreatorTargetTicket->save()
plugins/formcreator/inc/form_answer.class.php:748 PluginFormcreatorForm_Answer->generateTarget()
plugins/formcreator/inc/form.class.php:1220 PluginFormcreatorForm_Answer->saveAnswers()
plugins/formcreator/front/form.form.php:123 PluginFormcreatorForm->saveForm()

To Reproduce
Steps to reproduce the behavior:

1. create a form with a target ticket
2. add a group to actors of type "assigned"
3. Create a ticket template and set the same group to actors of type assigned
4. add the ticket template to the target ticket
5. Fill the form, an SQL error will occur

Expected behavior
No double group assignation to the ticket.

Either the double assignation must be detected, either the ticket template support should be removed. The second option is probably better, but requires the type of ticket (incident or request) be implemented in the plugin.