charm func test runner: fix broken target list

[lathiat]

The list of test targets was always "target" instead of the actual list
of targets due to an accidentally ommited $-sign in #230

[lathiat]

Without this fix, it tries to run the suite with --bundle target instead of --bundle jammy-caracal or similar.

func-target run-test: commands[0] | functest-run-suite --keep-model --bundle target
2024-09-11 07:11:42 [INFO] Could not determine correct model aliasfrom tests.yaml, using default
2024-09-11 07:11:43 [INFO] Deploying bundle '/home/ubuntu/src/charms/charm-glance-simplestreams-sync/tests/bundles/target.yaml' on to 'zaza-0c639d717a63' model
2024-09-11 07:11:43 [ERROR] {'default_alias': 'zaza-0c639d717a63'}
2024-09-11 07:11:43 [ERROR] Model default_alias (zaza-0c639d717a63)
Traceback (most recent call last):
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/bin/functest-run-suite", line 8, in <module>
    sys.exit(main())
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/func_test_runner.py", line 405, in main
    func_test_runner(
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/func_test_runner.py", line 313, in func_test_runner
    run_env_deployment(env_deployment, keep_model=preserve_model,
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/func_test_runner.py", line 145, in run_env_deployment
    deploy.deploy(
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/deploy.py", line 397, in deploy
    deploy_bundle(bundle, model, model_ctxt=model_ctxt, force=force,
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/deploy.py", line 359, in deploy_bundle
    for overlay in render_overlays(bundle_out or bundle, tmpdirname,
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/deploy.py", line 305, in render_overlays
    if should_render_local_overlay(bundle):
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/deploy.py", line 287, in should_render_local_overlay
    return is_local_overlay_enabled_in_bundle(bundle)
  File "/home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.10/site-packages/zaza/charm_lifecycle/deploy.py", line 258, in is_local_overlay_enabled_in_bundle
    with open(bundle, 'r') as stream:
FileNotFoundError: [Errno 2] No such file or directory: '/home/ubuntu/src/charms/charm-glance-simplestreams-sync/tests/bundles/target.yaml'
ERROR: InvocationError for command /home/ubuntu/src/charms/charm-glance-simplestreams-sync/.tox/func-target/bin/functest-run-suite --keep-model --bundle target (exited with code 1)
___________________________________ summary ____________________________________
ERROR:   func-target: commands failed
Destroy model and run next test? [ENTER]