Skip flaky test: test_multiple_items

[devinfra-flakiness]

tracking here: https://linear.app/getsentry/issue/DI-1008/flakiness-database-test-region-is-being-accessed-by-other-users

Please help us keep Sentry flake-free by merging this PR while a longer-term
resolution is implemented in issue #93979.

Test: tests/sentry/workflow_engine/processors/test_log_util.py::TestBatchPerformanceTracker::test_multiple_items

Statistics over the last 30 days:
* Runs Recorded: 645
* Flakes Failed: 0 (0%)
* Flakes Retried: 581 (90.077519%)

Example Flakes:

• https://github.com/getsentry/sentry/actions/runs/15785543753/job/44501035903
• https://github.com/getsentry/sentry/actions/runs/15785255109/job/44500166661
• https://github.com/getsentry/sentry/actions/runs/15785224553/job/44500079641
• https://github.com/getsentry/sentry/actions/runs/15785110905/job/44499732262
• https://github.com/getsentry/sentry/actions/runs/15784975654/job/44499306977

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See also:
Flaky Test Policy & Responsibilities

[kcons]

These are not failures from this test, these are the result of improper cleanup from other tests in the shard.

[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 🥀