cargo: use neon branch of rust-postgres

[VladLazar]

Problem

We are pining our fork of rust-postgres to a commit hash and that prevents us from making
further changes to it. The latest commit in rust-postgres requires #8747,
but that seems to have gone stale. I reverted rust-postgres neon branch to the pinned commit in neondatabase/rust-postgres#31.

Summary of changes

Switch back to using the neon branch of the rust-postgres fork.

cc: @conradludgate

[github-actions]

5400 tests run: 5173 passed, 0 failed, 227 skipped (full report)

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Code coverage* (full report)

• functions: 31.8% (7891 of 24837 functions)
• lines: 49.4% (62451 of 126324 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
043b8f5 at 2024-11-14T12:26:50.916Z :recycle:}