fix: Fix _archives creation

[limakzi]

While importing new package, if only _archives directory does not exists, the import wrongly fails.

gap-packagedistro on  main λ ./tools/import_packages.py https://limakzi.github.io/smallantimagmas/PackageInfo.g
downloading https://limakzi.github.io/smallantimagmas/PackageInfo.g to tempfile /tmp/pkginfouja6h7cs.g
update packages/smallantimagmas/meta.json
gap-packagedistro on  main λ rm -rvf _archives/
removed '_archives/smallantimagmas-0.2.3.tar.gz'
removed directory '_archives/'
gap-packagedistro on  main λ ./tools/import_packages.py https://limakzi.github.io/smallantimagmas/PackageInfo.g
downloading https://limakzi.github.io/smallantimagmas/PackageInfo.g to tempfile /tmp/pkginfoh_kpnblo.g
Traceback (most recent call last):
  File "/home/limakzi/documents/gap-packagedistro/./tools/import_packages.py", line 38, in <module>
    main(sys.argv[1:])
  File "/home/limakzi/documents/gap-packagedistro/./tools/import_packages.py", line 34, in main
    import_packages(pkginfo_paths)
  File "/home/limakzi/documents/gap-packagedistro/tools/scan_for_updates.py", line 115, in import_packages
    utils.download(url, archive_fname)
  File "/home/limakzi/documents/gap-packagedistro/tools/utils.py", line 55, in download
    with open(dst, "wb") as f:
         ^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '_archives/smallantimagmas-0.2.3.tar.gz'
gap-packagedistro on  main λ 

[fingolfin]

Thanks!