[FIX] stock_account: negative stock and vacuum

Running the vacuum in avco indeed fixed the estimated value on the
delivery but it did not update the standard price afterwards, making it
possible to have an inconsistent standard price with the actual value in
stock, as described in [0] and in the task [1].

A test was added (and validated) in the layers test file and an two old
one were fixed. test_average_perpetual_2 displayed also a different
missing bit: the vacuum should run when the user unlock and increments a
receipt.

[0] https://github.com/odoo/odoo/pull/41669


[1] 2154638

closes odoo/odoo#41766

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>