DPE-5625 chore: bump juju versions (#325)

## Issue


## Solution

Author: paulomach

.github/workflows/ci.yaml

@@ -73,18 +73,18 @@ jobs:
       fail-fast: false
       matrix:
         juju:
-          - agent: 2.9.50  # renovate: juju-agent-pin-minor
+          - agent: 2.9.51  # renovate: juju-agent-pin-minor
             libjuju: ^2
             allure_on_amd64: false
-          - agent: 3.4.5  # renovate: juju-agent-pin-minor
+          - agent: 3.5.4  # renovate: juju-agent-pin-minor
             allure_on_amd64: true
           - snap_channel: 3.6/beta
             allure_on_amd64: false
         architecture:
           - amd64
         include:
           - juju:
-              agent: 3.4.5  # renovate: juju-agent-pin-minor
+              agent: 3.5.4  # renovate: juju-agent-pin-minor
               allure_on_amd64: true
             architecture: arm64
           - juju: