The 'hirsute' key in c-h/core/host_factory/ubuntu.py:
UBUNTU_RELEASES had been missed out, and is needed for
hirsute support in many of the charms. This sync is to
add just that key. See also [1]
Note that this sync is only for classic charms.
[1] https://github.com/juju/charm-helpers/pull/598
Change-Id: Ice7eb3dee63f319d2b534a72fd228853e3bad9bd