Existing task test cases should be OSCAL version agnostic

[degenaro]

Describe the bug

Some task test cases do a file compare of generated OSCAL document with a pre-generated one, and will fail when OSCAL version changes since OSCAL version is embedded in the docs.

To Reproduce

Mock trestle code with a new version of OSCAL.

Expected behavior

The task test cases should not fail when OSCAL version changes.

Screenshots / Logs.

N/A

Environment

Nominal trestle install.

[fsuits]

Thanks @degenaro - yes ideally the tests would be resilient to changes in the oscal version as specified in trestle/oscal/__init__.py