APP-7889: Fixed handling of source_tag when no attributes present

[Aryamanz29]

✨ Description

https://atlanhq.atlassian.net/browse/APP-7889

🧩 Type of change

Select all that apply:

• 🚀 New feature (non-breaking change that adds functionality)
• 🐛 Bug fix (non-breaking change that fixes an issue) — please include tests! Refer testing-toolkit 🧪
• 🔄 Refactor (code change that neither fixes a bug nor adds a feature)
• 🧹 Maintenance (chores, cleanup, minor improvements)
• 💥 Breaking change (fix or feature that may break existing functionality)
• 📦 Dependency upgrade/downgrade
• 📚 Documentation updates

---

✅ How has this been tested? (e.g. screenshots, logs, workflow links)

Describe how the change was tested. Include:

• Steps to reproduce
• Any relevant screenshots, logs, or links to successful workflow runs
• Details on environment/setup if applicable

---

📋 Checklist

• My code follows the project’s style guidelines
• I’ve performed a self-review of my code
• I’ve added comments in tricky or complex areas
• I’ve updated the documentation as needed
• There are no new warnings from my changes
• I’ve added tests to cover my changes
• All new and existing tests pass locally

[Copilot]

Pull Request Overview

This PR fixes a bug in the source_tag handling where the code would fail when a tag had no attributes present. The fix adds proper null/existence checks before accessing nested attribute dictionaries.

• Updated the translator to safely check for attributes existence before accessing nested keys
• Enhanced test coverage to include scenarios for source tags with attributes, without attributes, and deleted source tags
• Modified test assertions to account for the additional test cases and different behavior patterns

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pyatlan/model/translators.py	Added null safety checks when accessing tag attributes to prevent crashes
tests/unit/test_atlan_tag_name.py	Enhanced test coverage with multiple source tag scenarios and updated assertions