eden-trusted: use eden master for EVE master CI

[eriknordmark]

Summary

• The tests-master job in eden-trusted.yml was pinned to eden tag 1.0.15, while eden master had moved two releases ahead (1.0.16 and beyond).
• This caused smoketest failures on PRs against EVE master when the issue was in eden, not EVE itself.
• Change the uses: ref for tests-master to @master so it always tracks eden master.
• The three stable-branch jobs (tests-13-4-stable, tests-14-5-stable, tests-16-0-stable) remain pinned to @1.0.15 as those EVE branches require the older compatible eden version.

Test plan

• Verify the failing smoketests in Fix lost NTP telemetry #5851 pass after this change
• Verify stable-branch CI jobs still reference @1.0.15 and are unaffected

🤖 Generated with Claude Code

[europaul]

@eriknordmark only the workflow file is checked out on 1.0.15, the rest of the eden repo incl tests is checked out on master.
I'm not against this change, but it will not solve any failing tests. The only change to the workflow file since 1.0.15 is lf-edge/eden@709f514 - and it doesn't solve anything.

[rene]

@europaul , I think it still makes sense to fetch test from master, we might have future changes only intend for master, so I think this keeps more "alignment" and also avoid confusions...