Add test coverage for team membership sync scripts

[Copilot]

The core team synchronization scripts (yaml_to_github.py, github_to_yaml.py) had no test coverage for their primary functionality.

Changes

• test_yaml_to_github.py (10 tests): Verifies YAML → GitHub sync behavior

  • Adding org members to teams
  • Inviting non-org members when adding to teams
  • Removing members from teams
  • Preventing duplicate invites

• test_github_to_yaml.py (13 tests): Verifies GitHub → YAML export behavior

  • Exporting team membership changes
  • Handling org member removals across all teams
  • Preserving pending invites during export
  • YAML rendering and state loading

All tests use mocked API responses to avoid live GitHub calls. Test count: 16 → 39.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tests to make sure scripts do what they are supposed</issue_title>
<issue_description>Monkey-patching the organization information, test if changes are what one would expect.

For the YAML:

• adding someone to a team that is in the org
• adding someone to a team that is not in the org
• remove someone from the team

For the GitHub settings:

• adding someone to a team that is in the org
• removing someone from a team
• removing someone from the org</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add tests to make sure scripts do what they are supposed #21

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[lubianat]

lgtm