pageserver: make RemoteTimelineClient::schedule_index_upload infallible

[erikgrinaker]

Remove an unnecessary Result and address a FIXME.

[github-actions]

7162 tests run: 6865 passed, 0 failed, 297 skipped (full report)

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Flaky tests (14)

Postgres 17

• test_pageserver_small_inmemory_layers[False]: debug-x86-64
• test_idle_checkpoints: debug-x86-64
• test_secondary_background_downloads: debug-x86-64
• test_physical_replication_config_mismatch_too_many_known_xids: debug-x86-64
• test_pageserver_metrics_removed_after_detach: debug-x86-64
• test_timeline_archival_chaos: release-x86-64, release-arm64, release-arm64, release-x86-64
• test_timeline_archive[4]: debug-x86-64

Postgres 15

• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64
• test_pgdata_import_smoke[8-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64
• test_create_churn_during_restart: release-x86-64

Postgres 14

• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64

Code coverage* (full report)

• functions: 31.4% (8401 of 26776 functions)
• lines: 48.1% (66623 of 138639 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
07df0b5 at 2024-12-16T15:44:26.857Z :recycle:}