The certificate handler code does a bit of work and should not
run during the update-status hook.
As documented in the charms.reactive dispatch [0] function
handlers registered with the @hook decorator will execute before
other handlers. So we can rely on the 'is-update-status-hook'
flag being consistently set when in update-status hook before
other handlers are evaluated for dispatch.
0: 3d27f3d24a/charms/reactive/bus.py (L325)
Closes-Bug: #1954748
Change-Id: I4a3aa544f98049c83db576f95de826038e8e1afc
93bc9e1837