fix: satisfy shellcheck in setup preview scripts

Amp-Thread-ID: https://ampcode.com/threads/T-01a17775-d386-7387-88ab-c14a99ed558e
Co-authored-by: Amp <amp@ampcode.com>

Author: ivanmilevtues

scripts/action/resolve-preview-prs.sh

@@ -30,7 +30,7 @@ line="$(grep -oE '<!-- codeboarding:preview [0-9, ]+ -->' <<< "$body" | head -n
 
 skip() { echo "::notice::Not previewing #$1: $2"; }
 seen=" "
-for pr in $(grep -oE '[0-9]+' <<< "${line#*preview}"); do
+while IFS= read -r pr; do
   [ "$count" -lt "$max" ] || { skip "$pr" "at most $max pull requests are previewed."; continue; }
   [ "$pr" != "$PR_NUMBER" ] || continue
   case "$seen" in *" $pr "*) continue ;; esac
@@ -53,5 +53,5 @@ for pr in $(grep -oE '[0-9]+' <<< "${line#*preview}"); do
     --arg title "$(jq -r '.title // ""' <<< "$json")" \
     '{pr_number: $pr, head_sha: $head_sha, merge_base_sha: $merge_base, title: $title}' > "$out/$count.json"
   prs="${prs:+$prs,}$pr"
-done
+done < <(grep -oE '[0-9]+' <<< "${line#*preview}")
 finish

scripts/action/review-preview-pr.sh

@@ -17,6 +17,7 @@ n="$1"
 dir="${RUNNER_TEMP:?}/codeboarding-preview"
 entry="$dir/$n.json"
 [ -f "$entry" ] || exit 0
+: "${REPOSITORY:?}"
 IFS=$'\t' read -r pr head_sha pr_merge_base < <(jq -r '[.pr_number, .head_sha, .merge_base_sha] | @tsv' "$entry")
 title="$(jq -r '.title' "$entry")"
 base="$REVIEW_BASE_SHA"