Teardown must not decide a test's verdict

Under set -e a failing command in an EXIT trap becomes the script's exit
status, so a cleanup hiccup fails a test whose assertions all passed. Run
teardown with errexit off, on EXIT only: sharing set +e with the signal
traps would leave errexit off for the rest of a signalled run, where a
torn-down test could still report success. A failing teardown command
still prints its own diagnostic, so nothing is silenced.

The return 0 that three cleanup() bodies ended with never protected
anything: errexit fires at the failing command before it is reached.

Closes #773

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Xavier Roche <xroche@gmail.com>

tests/13_crawl_proxy_https.test

@@ -31,7 +31,7 @@ cleanup() {
     done
     rm -rf "$tmpdir"
 }
-trap cleanup EXIT
+trap 'set +e; cleanup' EXIT
 
 # self-signed cert for the local TLS origin (httrack does not verify certs)
 openssl req -x509 -newkey rsa:2048 -keyout "$tmpdir/key.pem" \