test flake: `oximeter-db client::tests::test_single_node`

This test run failed:
https://github.com/oxidecomputer/omicron/pull/5974/checks?check_run_id=26826740891

This PR just changed one doc comment not related to oximeter so I assume it's unrelated.

The failure looks like this:

Failed to insert measurement row: DatabaseUnavailable("error sending request for url (http://[::1]:63865/?output_format_json_quote_64bit_integers=0&wait_end_of_query=1): connection error: Connection reset by peer (os error 131)")
stack backtrace:
   0: rust_begin_unwind
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/std/src/panicking.rs:645:5
   1: core::panicking::panic_fmt
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/panicking.rs:72:14
   2: core::result::unwrap_failed
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/result.rs:1654:5
   3: core::result::Result<T,E>::expect
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/result.rs:1034:23
   4: {async_fn#0}
             at ./src/client/mod.rs:3105:9
   5: {async_fn#0}<u16>
             at ./src/client/mod.rs:2991:67
   6: {async_fn#0}
             at ./src/client/mod.rs:3023:43
   7: {async_fn#0}
             at ./src/client/mod.rs:3195:56
   8: {async_block#0}
             at ./src/client/mod.rs:1247:14
   9: poll<&mut dyn core::future::future::Future<Output=()>>
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/future/future.rs:123:9
  10: poll<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/future/future.rs:123:9
  11: {closure#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:659:57
  12: with_budget<core::task::poll::Poll<()>, tokio::runtime::scheduler::current_thread::{impl#8}::block_on::{closure#0}::{closure#0}::{closure_env#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/coop.rs:107:5
  13: budget<core::task::poll::Poll<()>, tokio::runtime::scheduler::current_thread::{impl#8}::block_on::{closure#0}::{closure#0}::{closure_env#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/coop.rs:73:5
  14: {closure#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:659:25
  15: tokio::runtime::scheduler::current_thread::Context::enter
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:404:19
  16: {closure#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:658:36
  17: tokio::runtime::scheduler::current_thread::CoreGuard::enter::{{closure}}
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:737:68
  18: tokio::runtime::context::scoped::Scoped<T>::set
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/context/scoped.rs:40:9
  19: tokio::runtime::context::set_scheduler::{{closure}}
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/context.rs:176:26
  20: try_with<tokio::runtime::context::Context, tokio::runtime::context::set_scheduler::{closure_env#0}<(alloc::boxed::Box<tokio::runtime::scheduler::current_thread::Core, alloc::alloc::Global>, core::option::Option<()>), tokio::runtime::scheduler::current_thread::{impl#8}::enter::{closure_env#0}<tokio::runtime::scheduler::current_thread::{impl#8}::block_on::{closure_env#0}<core::pin::Pin<&mut core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>>, core::option::Option<()>>>, (alloc::boxed::Box<tokio::runtime::scheduler::current_thread::Core, alloc::alloc::Global>, core::option::Option<()>)>
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/std/src/thread/local.rs:284:16
  21: std::thread::local::LocalKey<T>::with
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/std/src/thread/local.rs:260:9
  22: tokio::runtime::context::set_scheduler
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/context.rs:176:9
  23: tokio::runtime::scheduler::current_thread::CoreGuard::enter
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:737:27
  24: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:646:19
  25: {closure#0}<core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:175:28
  26: tokio::runtime::context::runtime::enter_runtime
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/context/runtime.rs:65:16
  27: block_on<core::pin::Pin<&mut dyn core::future::future::Future<Output=()>>>
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/scheduler/current_thread/mod.rs:167:9
  28: tokio::runtime::runtime::Runtime::block_on
             at /home/build/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.37.0/src/runtime/runtime.rs:349:47
  29: test_single_node
             at ./src/client/mod.rs:1251:9
  30: oximeter_db::client::tests::test_single_node::{{closure}}
             at ./src/client/mod.rs:1077:32
  31: core::ops::function::FnOnce::call_once
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/ops/function.rs:250:5
  32: core::ops::function::FnOnce::call_once
             at /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

@bnaecker can you take a look (or do you know who else might be able to)?