[Bug] CKEditor 5 Link Attributes submodule: rel|nofollow results in rel="o" instead of rel="nofollow"

Problem after updating CKEditor 5 Plugin Pack 1.4.2 > 1.5.0

When using the Link Attributes feature from CKEditor 5 Plugin Pack, adding a rel attribute via the UI does not work correctly.

Specifically, when entering:

rel|nofollow

the resulting HTML output contains:

<a href="..." rel="o">...</a>

instead of the expected:

<a href="..." rel="nofollow">...</a>

This issue only affects the rel attribute.
Other attributes such as class|button work correctly and produce valid output.

Environment

- Drupal core: 10.6.2
- CKEditor 5 Plugin Pack: 1.5.0
- CKEditor 5 Link Attributes: enabled (from Plugin Pack)
- Text format: Full HTML
- PHP: 8.3

Steps to reproduce

1. Enable CKEditor 5 Plugin Pack (1.5.0).
2. Enable Link Attributes.
3. Go to Configuration → Content → Text formats and editors → Full HTML.
4. Ensure CKEditor 5 is enabled and Link Attributes button is available.
5. Create or edit content using Full HTML.
6. Insert a link.
7. Open Link Attributes dialog.
8. Add the attribute:

rel|nofollow

9. Save the content.
10. Inspect the rendered HTML.

Actual result

The link is rendered as:

<a href="..." rel="o">...</a>

Expected result

The link should be rendered as:

<a href="..." rel="nofollow">...</a>

Additional notes

- The issue only affects the rel attribute.
- Other attributes work correctly, for example:
class|button → class="button"
- Downgrading CKEditor 5 Plugin Pack to 1.4.2 fix the problem.
- The issue appears to be related to how the Link Attributes plugin parses the rel attribute value.