ci: Make CI compatible with juju controller 3.1.6

[jneo8]

The juju.model.deploy(bundle) command somehow cause error if the controller version is 3.1.6

---

Replace line

# This line is not workable if controller version is 3.1.6
ops_test.model.deploy(bundle)

with

juju_cmd = ["deploy", "-m", ops_test.model_full_name, str(bundle)]
rc, stdout, stderr = await ops_test.juju(*juju_cmd)

Reference

[dashmage]

nit: name of function could be changed to script_dir.

[Pjack]

LTGM, functional test pass in 2.9 & 3.1 good job.

[chanchiwai-ray]

LGTM if it's as a workaround. We should probably keep an eye on charmed-kubernetes/pytest-operator#116 since the root cause maybe fixed in a newer release.