Add fix for ingesting mixed tarballs

[bedroge]

We just had another issue with mixed tarballs that contain both init files and software installations, e.g.:

2025.06/init/eessi_archdetect.sh
2025.06/software/linux/x86_64/intel/skylake_avx512/modules/all/EESSI-extend/2025.06-easybuild.lua
2025.06/software/linux/x86_64/intel/skylake_avx512/modules/devel/EESSI-extend/2025.06-easybuild.lua

The tarball has software in its name, and the ingestion script would use the first file in the tarball to verify that this also has a /software/ directory in its path, which is not the case here. I've added a fix based on @boegel's suggestion from #142 (comment), but instead I'm using a grep -m 1 (this will not have to go through the entire tarball, which could take a long while for large tarballs), which looks for the first file in the tarball listing that actually has the same type as what's in the filename. If the result is empty, I'm falling back to the old method, to make sure that it at least uses something.