Automatic merge from submit-queue (batch tested with PRs 42058, 41160, 42065, 42076, 39338)

Juju: Fix shebangs in charm actions to use python3

**What this PR does / why we need it**:

This fixes the microbot and create-rbd-pv actions by reverting them back to python3. We accidentally switched them to python2 to match the boilerplate checker's expectations for python files.

It looks like hack/verify-boilerplate.sh does not check these since they don't have the .py extension, so we should be good with no changes there.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*:

https://github.com/juju-solutions/bundle-canonical-kubernetes/issues/212

**Special notes for your reviewer**:

**Release note**:

```release-note
Juju: Fix shebangs in charm actions to use python3
```