Add missing tests for python model verification

### Is this your first time submitting a feature request?

- [x] I have read the [expectations for open source contributors](https://docs.getdbt.com/docs/contributing/oss-expectations)
- [x] I have searched the existing issues, and I could not find an existing issue for this feature
- [x] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

### Describe the feature

### Problem
The function `verify_python_model_code` in `core/dbt/parser/models.py` currently lacks unit tests, as noted by a `# TODO: add a test for this` comment in the code.

### Proposed Solution
I plan to add unit tests to [tests/unit/parser/test_python_model_verification.py](cci:7://file:///e:/Personal%20Projects/OpenSource/dbt/dbt-core/tests/unit/parser/test_python_model_verification.py:0:0-0:0) to cover:
1. Valid python model code.
2. Python code improperly containing Jinja (to verify `ParsingError` is raised).

### Describe alternatives you've considered

_No response_

### Who will this benefit?

_No response_

### Are you interested in contributing this feature?

_No response_

### Anything else?

_No response_