Environment.environ instead of os.environ

[happz]

Pull Request Checklist

• implement the feature
• write the documentation
• extend the test coverage
• update the specification
• adjust plugin docstring
• modify the json schema
• mention the version
• include a release note

[gemini-code-assist]

Code Review

This pull request replaces direct usage of os.environ and os.getenv with a custom Environment.environ singleton across the codebase, enforcing this via new linter rules. Feedback highlights a critical issue where modifying Environment.environ directly introduces side effects due to its singleton nature, requiring the use of .copy() instead. Additionally, double lookups of environment variables in tmt/config/__init__.py and tmt/plugins/__init__.py should be simplified using assignment expressions.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.