fix(anta): Fixing the TypeError: '<' not supported between instances of 'NoneType' and 'str'

[vitthalmagadum]

Description

anta/anta/result_manager/init.py", line 298, in sort
self._result_entries.sort(key=lambda result: [getattr(result, field) for field in sort_by])
~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'NoneType' and 'str'

Fixes #1110

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have run pre-commit for code linting and typing (pre-commit run)
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (tox -e testenv)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codspeed-hq]

CodSpeed Performance Report

Merging #1113 will not alter performance

_{Comparing vitthalmagadum:bug/result_manager (92c0f61) with main (2ba75e4)}

Summary

✅ 22 untouched benchmarks

[carl-baillargeon]

LGTM. Tested locally:

    {
        "name": "dc1-leaf1a",
        "test": "VerifyInterfaceDiscards",
        "categories": [
            "interfaces"
        ],
        "description": "Verifies that the interfaces packet discard counters are equal to zero.",
        "result": "unset",
        "messages": [],
        "custom_field": null
    },
    {
        "name": "dc1-leaf1a",
        "test": "VerifyInterfaceDiscards",
        "categories": [
            "interfaces"
        ],
        "description": "Verifies that the interfaces packet discard counters are equal to zero.",
        "result": "unset",
        "messages": [],
        "custom_field": "Generated by AVD"
    },