mappings: freebsd renamed py311-yaml to py311-pyyaml

This was changed a few months ago

https://cgit.freebsd.org/ports/commit/?id=1a80ec7c2281900b82b228ee3a7b070c8ca4286e



but we seemed to be lucky finding the package under the old name
in the repos until today, when it was presumably fully purged by
some cleanup process.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>