Stock is not decremented if a product variation type is set to Local stock but at a specific variation the Always in stock field is enabled

I attach a patch for this and I raise the priority of the issue since it could lead to an incorrect stock level in the reports.

This is probably not the right way of approaching the problem as this is not what the always-in-stock was designed for.
always-in-stock is for products that are not stock-managed.
However, I am not marking this as works as designed because the use case is real. I think this can be a useful feature if the responsibility is moved to the availability checker.
I will update the title to: "Allow the purchase of out-of-stock items" This will need both an absolute setting. Always allow or a number. A bit like an arranged overdraft - so 10 will be: You are allowed to oversell 10 items.