[Functionality][Art Gallery Block] Validation of images uniqueness works wrong

[ChornaOksana]

Environment: Windows 10 Home, Google Chrome 124.0.6367.209.
Reproducible: always
Build found: 0006ced

Preconditions:

1. Open site
2. Log in as admin

Steps to reproduce

1. Go to admin panel
2. Click on History-коди tab
3. Create new historycode filling all mandatory fields or edit alredy existing Historycode
4. Scroll down to Art Gallery block
5. Upload few arts among which would be two identical images

Actual result
Admin can upload two or more identical images. Then admin can make slides with those images. And only in the end, when admin tries safe changes, the messages "Виникла помилка при оновленні history-коду" appears

Expected result
After trying to upload two identical images (Завантажити арти), message "Такий арт вже існує" appears

User story and test case links
E.g.: "User story #127