Write a unittest for get_full_manifest

[ChenyuLInx]

Description

Write unittest/s for get_full_manifest function, this will act as an example for writing more unittest in parser directory

You will likely need to

• constructing a Manifest object using fixture/functions generated in Create unit tests for SemanticManifest supported by a manifest fixture and utility builders #9665 and mock the loader.load() to return it directly.
• create some fixture/function to generate a RuntimeConfig.
• do some mocking for tracking.

Non-functional requirements

Please organize tests related to parser/manifest.py and util functions related to make it easier for the next person to find it.

Potential existing arts:

dbt-core/tests/unit/test_manifest.py

Line 108 in ebc22fa

class ManifestTest(unittest.TestCase):

[ChenyuLInx]

• Determine whether we want to refactor this function into a individual file after adding the unittest.