[add] change required on field state for import

__init__.py

 # Copyright 2021 Le Filament (<http://www.le-filament.com>)
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from . import models

models/__init__.py

+# Copyright 2021 Le Filament (<http://www.le-filament.com>)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from . import membership_line

models/membership_line.py

+# Copyright 2021 Le Filament (<http://www.le-filament.com>)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from odoo import models, fields
+
+
+class MembershipLine(models.Model):
+    _inherit = 'membership.membership_line'
+
+    state = fields.Selection(readonly=False,)