Confusion between uninstall hooks can apparently trigger errors during
uninstallation as two hooks can confuse one another?

In this here case, the issue triggered during the uninstall hook of
`account_accountant`, which apparently combines with the uninstall
hook of `industry_fsm_sale` to trigger an invalid in-memory state for
`project_project`. An implicit flush during the hook then blows up
with a check constraint error.

Flushing at the end of the `industry_fsm_sale` hook or at the start of
the `account_accountant` hook fixes the issue, so might as well flush
after each hook to ensure whatever they did using models is pushed to
the database and in good shape (hopefully).

Part-of: odoo/odoo#119606