Update buildstream to version 2.1.0 / rev 26 via SR 1116595
    
    https://build.opensuse.org/request/show/1116595
    by user dimstar + anag+factory
    Forwarded request #1113282 from iznogood
    
    - Update to version 2.1.0:
      + Support new architecture name "la64v100"
      + Fix race condition when downloading sources
      + Properly handle partial download errors
      + Fix regressed ETag handling to prevent redundant file downloads
      + Fix parsing remotes specified on the command line
      + Fix bug when tracking ref-less sources (like local sources)
        when using project.refs
      + Follow semantic versioning more strictly
      + New `bst build --retry-failed` feature
      + Fix parsing override-project-caches configuration
      + Fix crashes when instructed to only download from mirrors, and
        some sources have no mirrors defined
      + Drop unnecessary dependency on dateutil
      + Fix severe hangs when can occur when running out of disk
        space specifically whe