fix(review-runs): inherit errexit so a failed gh call can't shrink the corrections window

[tend-agent]

review-runs-corrections.sh collects the maintainer-correction signals that Step 4 of review-runs turns into "no maintainer corrections" in the tracking issue — which later runs read as ground truth under Gate 1. Two of its three collections loop gh calls inside a command substitution, and bash does not apply set -e inside one unless inherit_errexit is set. A gh failure in any but the final iteration was therefore dropped from the JSON while the script still exited 0, reporting the surviving iterations as the whole window.

The fix is shopt -s inherit_errexit next to the existing set -euo pipefail, so every command substitution in the script aborts on a failed call rather than each collection needing its own guard.

Two regression tests, both failing before the change and passing after:

• a 502 on the issues/comments endpoint (the first of the two the loop reads) — previously exited 0 with only the pulls/comments half present
• a 502 on the first of two candidate PRs' reviews — previously exited 0 with only the second PR's reviews present

Why the existing guard didn't cover this

The script already reasons about set -e and this loop. Its comment above CANDIDATES explains that the candidate list is pulled into its own assignment because a failed --search inline in the for word list is invisible to set -e, and test_a_failed_candidate_search_aborts_rather_than_reporting_no_reviews pins that. That guard is correct and unchanged — but it covers the word list, not the loop bodies, which are the calls this PR fixes.

The distinction is inherit_errexit, not pipefail. pipefail does propagate the loop's status out of the pipeline, so a failure on the last iteration was already caught; only earlier iterations were silently dropped. The observed asymmetry:

$ bash -c 'set -euo pipefail; O=$(for i in 1 2 3; do
    if [ "$i" = 2 ]; then cat /nope 2>/dev/null; else echo "$i"; fi
  done | tr "\n" ","); echo "REACHED [$O]"'
REACHED [1,3,]        # exit 0

$ bash -c 'set -euo pipefail; shopt -s inherit_errexit; ...same...'
                      # exit 1

The pre-fix test output shows the real shape — the script emitted a complete-looking payload ("reviews": [], comments missing one endpoint) on stdout with 502 Bad Gateway on stderr and status 0.

review-runs-corrections.sh is the only script in the repo with this shape; the other nine under plugins/tend-ci-runner/scripts/ have no multi-command substitution, so the change is scoped to this file.

Verified with uv run pytest (884 passed).