Autotest fixes

[david-yz-liu]

Motivation and Context

There were two bugs related to autotesting that instructors (and I) encountered.

1. The autotest settings client-side validation was (sometimes) reporting an error when a criterion was not selected for a test group.
2. Test groups that were timing out were still causing marks to be set for their associated criteria. (I encountered this as a consequence of testing Improve default error message when a test group times out markus-autotesting#471.

Your Changes

Description:

1. Ensured that a criterion value of null is permitted in the form. This replaces the old '' default value; this is consistent with the data pulled from the database, which has each test group object's criterion_id set to nil (not ''). I think this was the cause of the flakiness of this error.
   • Also, modified the criterion label to 'N/A' to better communicate what a blank value means.
2. Improve the check for timed-out test group results. Note that the previous code used .slice to check for specific error type values; I've modified this to look for any specified error type.

Type of change (select all that apply):

• Bug fix (non-breaking change which fixes an issue)

Testing

Tested manually. Added test cases for the second change.

Questions and Comments (if applicable)

Checklist

• I have performed a self-review of my own code.
• I have verified that the pre-commit.ci checks have passed.
• I have verified that the CI tests have passed.
• I have reviewed the test coverage changes reported on Coveralls.
• I have added tests for my changes.
• I have updated the Changelog.md file.