[BUG]: cannot update donations when inventory is below distribution

[jimmyli97]

Is there an existing issue for this?

• [X] I have searched the existing issues

Current Behavior

Related to #4172

After creating a distribution which decreases the inventory for an item, attempts to update donations which have that item fail with "Error updating donation: Requested items exceed the available inventory", even if the quantity for that item remains the same or increases.

Expected Behavior

It should let you update the donation if the quantity for that item remains the same or increases.

Steps To Reproduce

1. bin/setup followed by bin/start
2. In browser, create a distribution at a storage location which decreases the inventory for an item
3. In browser, attempt to update a donation which contains that item at that storage location

Environment

main commit 524eaa

Criteria for Completion

[] fix [] write tests

Anything else?

No response

Code of Conduct

• [X] I've read the Code of Conduct and understand my responsibilities as a member of the Ruby for Good community