test(settings): reduce flakiness of authorized group integration assertions

[joshtrichards]

Summary

This updates the DuplicateAssignmentIntegrationTest to avoid relying on unstable autoincrement ID equality in the integration DB environment. The test now focuses on verifying that the expected record exists with the correct groupId and class, which is more robust for sharded/integration-backed database runs.

This test was failing for me, in the Sharding database test integration work flow, for no discernible PR/branch specific reason:

There was 1 failure:

1) OCA\Settings\Tests\Integration\DuplicateAssignmentIntegrationTest::testMapperFindsExistingRecord
Failed asserting that 7 matches expected 0.

/home/runner/actions-runner/_work/server/server/apps/settings/tests/Integration/DuplicateAssignmentIntegrationTest.php:155

May be worth backporting, for the benefit of backport test runs (hah), since this code goes back to at least v31.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI