* ci: bump ubuntu from `f610ab9` to `68ee220` in /ci

Bumps ubuntu from `f610ab9` to `68ee220`.

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-version: '24.04'
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* ci(image): describe the Ubuntu index pin

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* ci(image): repin the pruned Neon User Edition stage

The 2026-09-12 Neon digest no longer resolves on invent-registry.kde.org,
so the CI image recipe could not be rebuilt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test(share): run the export test under the KDE platform theme

Neon's KF 6.31/Plasma 6.8 packages warn that Kirigami's breeze-internal
fallback icon theme is missing when no platform theme is set, which fails
the test's no-warning assertion in the refreshed CI image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* ci: pin the refreshed CI runtime image

Published by CI image run 39985699563 from 8a0e286.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Simone <lucenz@proton.me>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>