Skip flaky test: test_uptime_root_tree_with_orphaned_spans

[devinfra-flakiness]

Please help us keep Sentry flake-free by merging this PR while a longer-term
resolution is implemented in issue #97781.

Test: tests/snuba/api/endpoints/test_organization_trace.py::OrganizationEventsTraceEndpointTest::test_uptime_root_tree_with_orphaned_spans

Statistics over the last 30 days:
* Runs Recorded: 266
* Flakes Failed: 1 (0.37594%)
* Flakes Retried: 56 (21.052632%)

Example Flakes:

• https://github.com/getsentry/sentry/actions/runs/16916552191/job/47931794687
• https://github.com/getsentry/sentry/actions/runs/16941257710/job/48010741821
• https://github.com/getsentry/sentry/actions/runs/16941139672/job/48010326910
• https://github.com/getsentry/sentry/actions/runs/16940925378/job/48009544198
• https://github.com/getsentry/sentry/actions/runs/16939762805/job/48005442078

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See also:
Flaky Test Policy & Responsibilities

[floels]

Proposed a fix here: #97831

[getsantry]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀