Before this commit executing m2m commands in batch would lead to undesired
results, such as duplicating the related records on every subsequent record of
the batch.
Indeed since [1] the `create` and `unlink` are called in a loop, but their
content was not reset at each iteration.
[1] 9920f20e4cclosesodoo/odoo#43950
X-original-commit: 0800f64b011c8f020c0d7dd6e1c149aebd1a4627
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>