Fix ProductionRun.appliance docstring

[denizs]

Currently, the ProductionRun model's appliance member is documented as the appliance UUID, while it is actually an Appliance model. This PR fixes this.

[github-actions]

Coverage results

This is the coverage report for commit b3495a6

Name                                                                                Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------------------------------------------------
.tox/py/lib/python3.12/site-packages/enlyze/__init__.py                                 4      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/base.py                        65      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/client.py      20      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/production_runs/models.py      51      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/client.py           19      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/api_clients/timeseries/models.py           34      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/auth.py                                    13      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/client.py                                  86      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/constants.py                                6      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/errors.py                                   3      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/models.py                                 108      0   100%
.tox/py/lib/python3.12/site-packages/enlyze/validators.py                              38      0   100%
-----------------------------------------------------------------------------------------------------------------
TOTAL                                                                                 447      0   100%

4 empty files skipped.