Update minor upgrade tests and fix issues

[phvalguima]

Minor upgrade tests started failing after moving to newer snap revisions. Besides, we need to enforce a test of the following scenarios: 2.12.0 > newest built charm 2.13.0 > newest built charm 2.14.0 > newest built charm

And we need to do it for both small and large deployments.

[github-actions[bot]]

https://warthogs.atlassian.net/browse/DPE-4454

[phvalguima]

Closed with #315