fix: Fix not being able to change or remove banner

[steverydz]

Done

Fixes issue where banners are unable to be removed or changed

How to QA

Remove a banner image:

• Go to https://snapcraft-io-5431.demos.haus/<SNAP_NAME>/listing
• Remove the banner image and save the form
• Check that it saves successfully
• Reload the page
• The banner should not be there

Upload a banner image when there isn't already one there:

• Upload a banner image and save the form
• Check that it saves successfully
• Reload the page
• The new banner should be there

Change an existing banner image:

• Change an existing banner to a new image and save the form
• Check that it saves successfully
• Reload the page
• The updated banner should be there

Testing

• This PR has tests
• No testing required (explain why): Existing tests

Issue / Card

Fixes https://warthogs.atlassian.net/browse/WD-30391
Fixes #5430

[webteam-app]

Demo

Jenkins

demos.haus

[Copilot]

Pull Request Overview

This PR fixes a bug preventing users from changing or removing banner images in the publisher interface. The issue stemmed from conflicts in the changes.images array during form submission that caused a "modified during validation" error.

Key changes:

• Filters out existing banner entries from changes.images when banner field is dirty to prevent override conflicts
• Updates banner URL in changes.images when banner_urls field changes to ensure the new URL is properly persisted

[bartaz]

Didn't you just remove the banner from changes.images in line 54? Or is it different case?

[steverydz]

@bartaz Yeah, these are two different cases - banner and banner_urls are two different cases, which is confusing, but if banner changes that means the banner has been removed, and if banner_urls changes, that means one has been uploaded. I wasn't able to find a scenario where these fields would change at the same time.

[bartaz]

Maybe worth adding this to (already useful) comments you added to the code. To clarify which one changes when.

[bartaz]

LGTM, but maybe worth waiting for cache hotfix to land first before merging this, just to be sure.