deposit: accordion does not pick up nested errors

[mugraph]

Package version (if known): v4.10.1

Describe the bug

In AccordionField.js nested errors that are not objects with message and severity keys are not collected. While the FormFeedback component lists errors in a respective section, its accordion header is not aware of the contained errors.

Steps to Reproduce

1. Go to 'New upload' in the demo instance
2. Scroll down to e.g. the Alternate identifiers section
3. Select a Scheme but do not provide an identifier
4. Hit 'Save draft'
5. Expect the error to be indicated in the Form Feedback banner
6. Expect the accordion to be highlighted (it is not)

Screenshots (if applicable)

Additional context