fix(per-tenant throttling): incorrect allowed_rps field in log message

[problame]

The refill_interval switched from a milliseconds usize to a Duration during a review follow-up, hence this slipped through manual testing.

Part of #5899

[github-actions]

2466 tests run: 2345 passed, 0 failed, 121 skipped (full report)

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Flaky tests (3)

Postgres 16

• test_remote_timeline_client_calls_started_metric: debug

Postgres 15

• test_remote_storage_upload_queue_retries: debug
• test_timeline_size: debug

Code coverage* (full report)

• functions: 28.8% (6756 of 23462 functions)
• lines: 47.6% (41077 of 86306 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
28359fb at 2024-02-22T08:42:44.216Z :recycle:}