[IMP] hr_holidays: Test access rights post install

Some module can inherit leave models and override some methods.
The overridden method could access some models which require other
access level.
In this case, the access issues would not be found by tests because
other modules are not yet installed.

e.g.
Recently, the `_create_resource_leave` was overridden in hr_payroll and
is reading the employee's contract. A HR user approving a leave
would raise an access error because he doesn't have contract rights.
If the tests would have been executed post install, this bug would
have been detected.

addons/hr_holidays/tests/test_access_rights.py

@@ -10,7 +10,7 @@ from odoo.exceptions import AccessError, ValidationError, UserError
 from odoo.tools import mute_logger
 
 
-@tests.tagged('access_rights')
+@tests.tagged('access_rights', 'post_install', '-at_install')
 class TestLeavesRights(TestHrHolidaysBase):
 
     def setUp(self):