Pin juju to 2.9/stable

Change-Id: Idad2effb3ce9ac4f2a8e942bff8f6502d521b501
diff --git a/playbooks/setup-juju-client/pre.yaml b/playbooks/setup-juju-client/pre.yaml
index fdcd76b..25aca2c 100644
--- a/playbooks/setup-juju-client/pre.yaml
+++ b/playbooks/setup-juju-client/pre.yaml
@@ -1,13 +1,14 @@
 - hosts: all
   tasks:
+  # TODO: We require 2.9/stable: https://bugs.launchpad.net/juju/+bug/1974256
   - name: Install juju
-    ansible.builtin.command: snap install juju --classic
+    ansible.builtin.command: snap install juju --classic --channel=2.9/stable
     become: true
 
   - name: Log In to the Controller
     no_log: true
     block:
-      # Needed because: https://bugs.launchpad.net/juju/+bug/1995697
+      # TODO: Needed because: https://bugs.launchpad.net/juju/+bug/1995697
       - name: Ensure '~/.local/share' exists
         ansible.builtin.file:
           path: "{{ ansible_env.HOME }}/.local/share"