fix: update Cargo.lock to fix cargo audit vulnerabilities (#1190)

## Summary

- Update `rustls-webpki` 0.103.10 → 0.103.12 (fixes RUSTSEC-2026-0098
and RUSTSEC-2026-0099: name constraint bypass vulnerabilities in TLS
certificate validation)
- Update `rand` 0.8.5 → 0.8.6 and 0.9.2 → 0.9.4 (fixes
RUSTSEC-2026-0097: unsound aliased mutable reference when using custom
loggers)

These were causing the [cargo audit CI job to
fail](https://github.com/DataDog/datadog-lambda-extension/actions/runs/24472752003/job/71517081151).

Only `Cargo.lock` is updated (no `Cargo.toml` changes needed — these are
transitive dependency version bumps).

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: lym953