Python: New tests for azure_cosmos_db_mongodb_collection and local_step

[gaudyb]

Motivation and Context

Improve coverage for azure_cosmos_db_mongodb_collection and local_step classes.

Description

New test files:

• test_azure_cosmos_db_mongodb_collection.py
• test_local_step.py

Contribution Checklist

• [ ] The code builds clean without any errors or warnings
• [ ] The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• [ ] All unit tests pass, and I have added new tests where possible
• [ ] I didn't break anyone :smile:

[markwallace-microsoft]

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3465	5 :zzz:	0 :x:	0 :fire:	1m 30s :stopwatch: