build: deny async-std and friends

[koivunej]

rationale: some crates pull these in as default; hopefully these hints will require less cleanup-after and Cargo.lock file watching.

follow-up to #5848.

[koivunej]

I failed to check (or parse the 5k line output): https://github.com/neondatabase/neon/actions/runs/6825817145/job/18564454476#step:11:63

error[banned]: crate 'async-channel = 1.9.0' is explicitly banned

I could set the --hide-inclusion-graph so the output would be readable. Trying that before removing the async-{channel,lock} deny.

After --hide-inclusion-graph: https://github.com/neondatabase/neon/actions/runs/6826007887/job/18565016413?pr=5849

[github-actions]

2376 tests run: 2258 passed, 0 failed, 118 skipped (full report)

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Flaky tests (3)

Postgres 16

• test_competing_branchings_from_loading_race_to_ok_or_err: debug
• test_ondemand_download_timetravel[local_fs]: debug

Postgres 15

• test_emergency_mode: release

Code coverage (full report)

• functions: 54.7% (8926 of 16330 functions)
• lines: 81.5% (51326 of 62999 lines)

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_{The comment gets automatically updated with the latest test results
a50222d at 2023-11-10T15:15:13.356Z :recycle:}