Tests fail with ruamel.yaml 0.18.0

### Environment

* Python version: 3.11.
* PyKwalify version: 1.8.0

### Steps to Reproduce

1. `git clone https://github.com/Grokzen/pykwalify.git && cd pykwalify`
2. `pip install -r dev-requirements.txt`
3. `pytest`

### Expected Behavior

Tests to run successfully

### Observed Behavior

Errors like the following are observed in a handful of tests:

```
E AttributeError:
E "safe_load_all()" has been removed, use
E
E yaml = YAML(typ='safe', pure=True)
E yaml.load_all(...)
E
E instead of file "/home/lily/src/pykwalify/tests/test_core.py", line 582
E
E yaml_data = yaml.safe_load_all(stream)
```

```
E AttributeError:
E "safe_dump()" has been removed, use
E
E yaml = YAML(typ='safe', pure=True)
E yaml.dump(...)
E
E instead of file "/home/lily/src/pykwalify/tests/test_unicode.py", line 50
E
E source_f.write(yaml.safe_dump(fail_data_2s_yaml, allow_unicode=True))
```