Fallback in packaging.get_user_site_packages() in environments that do not have user home eg. some CI

[blackandred]

Traceback (most recent call last):
  File "/usr/local/bin/rkd", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/dist-packages/rkd/bootstrap.py", line 108, in main
    app.main(argv=sys.argv)
  File "/usr/local/lib/python3.8/dist-packages/rkd/bootstrap.py", line 64, in main
    self._ctx = ContextFactory(io).create_unified_context(additional_imports=preparsed_args['imports'])
  File "/usr/local/lib/python3.8/dist-packages/rkd/context.py", line 257, in create_unified_context
    get_user_site_packages() + '/usr/share/rkd/internal',
  File "/usr/local/lib/python3.8/dist-packages/rkd/packaging.py", line 64, in get_user_site_packages
    return next(p for p in sys.path if 'site-packages' in p)
StopIteration
Error: Process completed with exit code 1.