sync: fix range recovery test vector

[zclawz]

Fixes the macOS test (macos-latest) CI failure from https://github.com/blockblaz/zeam/actions/runs/29247771524/job/86810099947.

Summary

• correct the forkMismatchRecoveryStart re-anchors to a recent justified ancestor test vector that failed in the macOS unit-test job
• the previous fixture used anchor slot 9339 with peer head 14735, which is outside the 3600-slot blocks_by_range serving window, so the helper correctly returned null
• the updated fixture keeps the peer head but uses a recent anchor/start pair inside the serving window, matching the test name and helper contract

Validation

• zig fmt --check pkgs/node/src/blocks_by_range_sync.zig
• git diff --check
• local workspace Zig 0.16 zig build test --summary all still fails in this runner because rustup is not installed, but the macOS failure signature from the linked job (expected 9340, found null) is gone from the local log.

[ch4r10t33r]

LGTM