flaky chutney test

Seen in a coverage-aggregated job https://gitlab.torproject.org/tpo/core/arti/-/jobs/486179:

+ CHUTNEY_PATH=/builds/tpo/core/arti/chutney
+ export CHUTNEY_PATH
+ source tests/chutney/arti.run
++ target=networks/basic
+ '[' -n '' ']'
+ target=networks/basic
+ /builds/tpo/core/arti/chutney/chutney stop /builds/tpo/core/arti/chutney/networks/basic
Launching chutney using Python 3.11.2
Sending SIGINT to nodes
Waiting for nodes to finish.
..
Waiting for nodes to cleanup and exit.
+ source tests/chutney/arti.run
++ target=networks/basic
./tests/chutney/teardown: line 39: result: parameter null or not set
Running after_script