test harness: fix not honoring one_test_case_per_file

I regressed this in 9aa431cba34699ae35f7905398a0c8263b2ad453.

thanks @topolarity for pointing out the issue
12e1304805Andrew Kelley committed on 3/29/2022, 7:20:10 PMparent9aa431c
1 file changedLine totals unavailable