tests: more allowed errors for test_safekeeper_migration

[DimasKovas]

Problem

Pageserver now writes errors in the log during the safekeeper migration. Some errors are added to allowed errors, but "timeline not found in global map" is not.

• Will be properly fixed in pageserver: handle connection errors during safekeeper migration #12191

Summary of changes

Add "timeline not found in global map" error in a list of allowed errors in test_safekeeper_migration_simple

[github-actions]

8661 tests run: 8035 passed, 0 failed, 626 skipped (full report)

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Flaky tests (1)

Postgres 17

• test_storage_controller_compute_hook_keep_failing: release-arm64-without-lfc

Code coverage* (full report)

• functions: 35.5% (8650 of 24375 functions)
• lines: 46.6% (69455 of 148955 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ac1e0b9 at 2025-07-08T09:19:24.857Z :recycle:}