- require python3-importlib-metadata for python < 3.8 (boo#1219652)

- Update to 2.2.6:
* FIX: extended variables were not correctly written if content of file
hadn't changed and file was read-only (API 201).
* FIX: failed parsing of arguments would return code 2 for warnings
instead of 1 for errors
* FIX: quoting variables where not correctly propagated when set from
the command line (API 201).
* FIX: some new functions were needed with higher security level and
had to be sorted accordingly (API 201).
* FIX: test action would fail with empty error message when using API
201
* FIX: timezone was not always correctly calculated in countries with
historically changing DST, closes #902
* NEW: add environment variable RDIFF_BACKUP_API_VERSION to
artificially modify the API version dictionary, see the man page for
details.
* NEW: add warning that server will be called with deprecated CLI and
how to avoid the corresponding warning (see also the FAQ)
* NEW: there is now a weekly release with changelog for intermediate
testing available at
https://github.com/rdiff-backup/rdiff-backup/releases/tag/weekly
* FIX: cross-version issue with 2.0.5 complaining about KeyError
restrict_path, closes #872
* FIX: fail gracefully when connection(s) can't be setup e.g. in case
of network error, closes #868

- Require python3-PyYAML, python3-pylibacl, python3-xattr
(the latter two were Recommends only; all are runtime dependencies).