Fix: Treat HTTP 410 as dead link in provider status mappings (#5466)

[Chavandeep]

Priority: Medium

Fixes

Fixes #5466 by @t-hamano

Description

This PR updates the dead link filtering logic to correctly treat HTTP 410 (Gone) responses as dead links.
Previously, such images were still returned by the API, causing missing previews and insertion errors in the WordPress block editor.

Changes

• Added dead status mapping in api/utils/check_dead_links/provider_status_mappings.py
  → now includes 410 (Gone), 404, 451, and common 5xx errors.
• Added regression test in api/test/utils/test_check_dead_links.py
  → ensures 410 is always recognized as a dead link.

Testing Instructions

1. Run the API test suite (pytest api/test/utils/test_check_dead_links.py), or rely on CI.
2. Verify that 410 is included in the dead status codes.
3. Confirm CI pipeline passes.

Checklist

• My pull request has a descriptive title.
• My pull request targets the default branch of the repository (main).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made.
• I added or updated documentation (not applicable).
• I tried running the project locally and verified no visible errors (relied on CI).
• I ran the DAG/media property docs generator (not applicable here).