[stable2509] Backport #10541: test-utils/fix: Parachains test-utils relay parent descendants mock data

[paritytech-release-backport-bot]

Backport #10541 into stable2509 from lexnv.

See the documentation on how to use this bot.

[paritytech-release-backport-bot]

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-10541-to-stable2509
git worktree add --checkout .worktree/backport-10541-to-stable2509 backport-10541-to-stable2509
cd .worktree/backport-10541-to-stable2509
git reset --hard HEAD^
git cherry-pick -x 0f28d8104be04cb13ac39ccfd17240f703953c33
git push --force-with-lease

[github-actions]

This pull request is amending an existing release. Please proceed with extreme caution,
as to not impact downstream teams that rely on the stability of it. Some things to consider:

• Backports are only for 'patch' or 'minor' changes. No 'major' or other breaking change.
• Should be a legit fix for some bug, not adding tons of new features.
• Must either be already audited or not need an audit.

Emergency Bypass

If you really need to bypass this check: add validate: false to each crate
in the Prdoc where a breaking change is introduced. This will release a new major
version of that crate and all its reverse dependencies and basically break the release.

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/20129523997
Failed job name: test-linux-stable