Juju should be pinned to 2.9 in charm-deployment-guide in the short term

[Nobuto Murata]

It's similar to https://bugs.launchpad.net/charm-deployment-guide/+bug/2015683, but it's a bit more urgent to take a measure in the very short term.

Juju snap switched the default channel to 3.1.

$ snap info juju
...
channels:
  3.1/stable: 3.1.5 2023-06-27 (23354) 77MB -
  3.1/candidate: ^
  3.1/beta: ^
  3.1/edge: 3.1.6-ad7c2e8 2023-08-01 (23810) 79MB -

However, there are many places in the deployment guide where 2.9 specific commands (juju add-relation, juju run). We should pin to 2.9 by having:

sudo snap install juju --classic --channel 2.9

instead of:

sudo snap install juju --classic

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-----------------------------------
Release: 0.0.1.dev510 on 2023-06-16 22:30:47
SHA: fc7c83f5ecdfe05207cf8d6ef71743e2104c6547
Source: https://opendev.org/openstack/charm-deployment-guide/src/deploy-guide/source/install-juju.rst
URL: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/install-juju.html

[Nobuto Murata (nobuto)]

https://review.opendev.org/c/openstack/charm-deployment-guide/+/890265

[Nobuto Murata (nobuto)]

Backports:
https://review.opendev.org/q/%2522Pin+to+Juju+2.9+for+the+time+being%2522

[Peter Matulis (petermatulis)]

Thanks a lot for this Nobuto.