[59_maintenance] chore: update webpki dependencies to fix cargo audit CI (#11793)

# Which issue does this PR close?

- Part of #11664 (59.3.2 release)

# Rationale for this change

The `Audit` job fails on pushes to `59_maintenance` (for example
https://github.com/apache/arrow-rs/actions/runs/39722525650/job/119639022597)
because two advisories were published against versions pinned in the
committed `Cargo.lock`:

- RUSTSEC-2026-0382: `rustls-webpki` 0.103.15 (fixed in 0.103.16)
- RUSTSEC-2026-0381: `webpki-roots` 1.0.7 (fixed in 1.0.10)

This is the same fix as #11752 on `main`.

# What changes are included in this PR?

Update only the two flagged crates in `Cargo.lock`:

```
cargo update -p rustls-webpki -p webpki-roots
```

Verified locally that `cargo audit --ignore RUSTSEC-2026-0194 --ignore
RUSTSEC-2026-0195` (the CI invocation) passes, and that the lockfile
resolves with `cargo +1.85.0 metadata --locked`. Both new versions have
`rust-version = "1.71"`, below the workspace MSRV of 1.85.

# Are these changes tested?

CI

# Are there any user-facing changes?

No. This only affects the lockfile used for workspace builds and CI.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: alamb