tests: libvirt-ci: Update to commit 'c8971e90ac' to pull in mformat and xorriso

tests: libvirt-ci: Update to commit 'c8971e90ac' to pull in mformat and xorriso

Pull in the following changes from lcitool:

* tests/lcitool/libvirt-ci 85487e1...c8971e9 (18):
  > mappings: add new package mappings for mformat and xorriso
  > docs: testing: Update contents with tox
  > .gitlab-ci.yml: Always test against installed lcitool
  > gitlab-ci.yml: Start using tox for testing
  > tox: Allow running with custom pytest options with {posargs}
  > gitignore: Add the default .tox directory
  > dev-requirements: Reference VM requirements
  > requirements: Add tox to dev-requirements.txt and drop pytest and flake
  > test-requirements: Rename to dev-requirements.txt
  > Add tox.ini configuration file
  > tests: commands: Consolidate the installed package/run from git tests
  > Add a pytest.ini
  > facts: targets: Drop Fedora 36 target
  > gitlab-ci.yml: Add Fedora 38 target
  > facts: targets: Add Fedora 38
  > facts: mappings: Drop 'zstd' mapping
  > facts: projects: nbdkit: Replace zstd mapping with libzstd
  > docs: mappings: Add a section on the preferred mapping naming scheme

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Message-Id: <20230504154611.85854-2-anisinha@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>