tests: bump up the allowed number of reads

tests: bump up the allowed number of reads
Kyle's OpenBSD buildslave used 41 reads when doing this test. The fact that I'm blindly bumping this number up to match the observed behavior probably means this isn't a good criterion to be testing for anyway. But perhaps someone else (Brian) could investigate why that run on Kyle's OpenBSD box took four more reads than we expected, and whether the fact that it took 41 reads to do this operation is indicative of an actual problem.