shell/caucase.sh: Silence a shellcheck warning.

In shell/caucase.sh line 1134:
    trap "kill \"$caucased_pid\"; wait; rm -rf \"$tmp_dir\"" EXIT
                 ^-----------^ SC2064: Use single quotes, otherwise this expands now rather than when signalled.
                                                 ^------^ SC2064: Use single quotes, otherwise this expands now rather than when signalled.

These variables are local, so immediate expantion is expected.

shell/caucase.sh

@@ -1129,6 +1129,7 @@ EOF
     caucased_dir="$tmp_dir/caucased"
     caucased --db "$caucased_dir/db.sqlite" --netloc "$netloc" &
     caucased_pid="$!"
+    # shellcheck disable=SC2064
     trap "kill \"$caucased_pid\"; wait; rm -rf \"$tmp_dir\"" EXIT
     if cd "$tmp_dir"; then
       :