test: validate upstream refresh cycle

[vitormattos]

Purpose

Validate the complete Nextcloud upstream refresh cycle with a controlled stale pin.

This PR intentionally moves only lint-eslint.yml to the previous Nextcloud revision:

• pinned upstream commit: 98dc00f32e5c4b85361a06a40c7f8d7d1c0a38f3
• vendored source matches that commit;
• SHA-256 matches that source;
• the materialized LibreCode template is rendered from that old source with the existing minimal patch.

The current Nextcloud revision for this file is 74cadeba1fd707e6a7ae193a8659e6834d6dc2c7.

Expected refresh result

Running Refresh upstream workflows on this branch should:

1. resolve the latest commit for nextcloud/.github:master:workflow-templates/lint-eslint.yml;
2. update upstream/sources.json from 98dc00f... to 74cadeba...;
3. store the new immutable raw URL and SHA-256;
4. replace the vendored source;
5. reapply patches/nextcloud/lint-eslint.yml.patch;
6. regenerate workflow-templates/lint-eslint.yml;
7. open the automated refresh PR.

This PR is a validation fixture only and should not be merged.