Explicitly set H5A_iterate_vers = 2
Explicitly set H5A_iterate_vers = 2

For some reason the fix in "HIDE deprecated HDF5 API"
(commit 5ebd9f52b39c2c5156b4b9363c14928fb4ad3737)
does not completely change the API used, leading to a segfault
when running the tests. This fixes the segfault.

chrisemblhh/nexus,chrisemblhh/nexus,nexusformat/code,nexusformat/code,chrisemblhh/nexus,nexusformat/code,nexusformat/code,chrisemblhh/nexus,nexusformat/code,chrisemblhh/nexus