Postgresql-k8s unit goes to blocked state: `Cannot disable plugins: Existing objects depend on it`

## Steps to reproduce

This only happens once per couple of test runs, hence is difficult to reproduce, but you can do so by running:
```
git clone https://github.com/canonical/iam-bundle.git
tox -e integration -- --keep-models
```

## Expected behavior
Postgresql-k8s app and unit get active.

## Actual behavior

At times `postgresql-k8s` unit gets stuck in blocked state, causing our bundle tests to fail. These are runs from this week:
https://github.com/canonical/iam-bundle/actions/runs/10880493814/job/30244416338#step:4:667
https://github.com/canonical/iam-bundle/actions/runs/10937282732/job/30362792991
https://github.com/canonical/iam-bundle/actions/runs/10900084647/job/30246933947
```
postgresql-k8s/0 [idle] blocked: Cannot disable plugins: Existing objects depend on it. See logs
```
However, we don't enable or disable any plugins in the charms integrated with the database (kratos and hydra). Could you advise what could be causing this?

## Versions

Operating system: ubuntu 22.04

Juju CLI: 3.4/stable

Juju agent: 3.4.5

Charm revision: 381

microk8s: 1.27 and 1.28/stable

## Log output

Juju debug log:
https://github.com/canonical/iam-bundle/actions/runs/10880493814/job/30244416338#step:14:1

## Additional context

We've been deploying postgresql-k8s from `14/stable` channel. So far the tests run successfully when it pointed to rev281, we're experiencing this flaky issue since it was promoted to rev381.

Start with the integration command `tox -e integration -- --keep-models` and the linked Juju debug log, then compare behavior between charm revisions 281 and 381. Trace the intermittent `Cannot disable plugins` state in the PostgreSQL-k8s unit and verify that the integration runs leave the app and unit active without blocked failures.

Written by the indexing model from the issue text.