apollo_gateway: stop auto-discovering bench helper as a bench target

[avi-starkware]

benches/utils.rs is a helper module included by benches/main.rs (the explicit
[[bench]], gated on the testing feature). Cargo's bench auto-discovery also
picked utils.rs up as a standalone, feature-less bench target, so
cargo bench/cargo clippy --benches failed to compile it without
--features testing (it references apollo_gateway::test_utils). Set
autobenches = false so only the explicit [[bench]] is a bench target.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[avi-starkware]

• apollo_gateway: stop auto-discovering bench helper as a bench target #14878 👈 (View in Graphite)
• workspace: emit line-tables-only debuginfo in dev profile #14877
• main-v0.14.3

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[cursor]

PR Summary

Low Risk
Packaging-only Cargo.toml change; no runtime or gateway logic affected.

Overview
Sets autobenches = false on apollo_gateway so Cargo only builds the declared [[bench]] (benches/main.rs, behind the testing feature).

Without this, auto-discovery also treated benches/utils.rs as its own bench crate. That helper is only meant to be mod utils from main.rs and depends on apollo_gateway::test_utils, so cargo bench / cargo clippy --benches failed when testing was not enabled.

^{Reviewed by Cursor Bugbot for commit a95b06d. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Yoni-Starkware]

@Yoni-Starkware reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on avi-starkware).