Skip running clippy in --release mode.

[hlinnaka]

It's pretty expensive to run, and there is very little difference between debug and release builds that could lead to different clippy warnings.

This is extracted from PR #8912. That PR wandered off into various improvements we could make, but we seem to have consensus on this part at least.

[github-actions]

4994 tests run: 4830 passed, 0 failed, 164 skipped (full report)

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Flaky tests (7)

Postgres 17

• test_pageserver_compaction_smoke: release-arm64
• test_ondemand_wal_download_in_replication_slot_funcs: release-x86-64
• test_pg_regress[4]: debug-x86-64
• test_scrubber_physical_gc_ancestors_split: release-x86-64

Postgres 16

• test_ondemand_wal_download_in_replication_slot_funcs: release-x86-64

Postgres 15

• test_scrubber_physical_gc[4]: release-arm64

Postgres 14

• test_subscriber_restart: release-x86-64

Code coverage* (full report)

• functions: 31.9% (7425 of 23300 functions)
• lines: 49.8% (59759 of 119904 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
aad550f at 2024-09-20T13:57:58.662Z :recycle:}