fix: default output to github on GitHub Actions

[ianlewis]

Description:

Default the --output flag to github when GITHUB_ACTIONS is true for ease of use on GitHub Actions.

Related Issues:

Fixes #1459

Checklist:

• [x] Review the CONTRIBUTING.md documentation.
• [x] Add a reference to a related issue in the repository.
• [x] Add a description of the changes proposed in the pull request.
• [x] Add unit tests if applicable.
• [x] Update documentation if applicable.
• [x] Add a note in the CHANGELOG.md if applicable.
• [x] Sign the Google CLA.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7018702) 79.04% compared to head (ccf2f7f) 79.16%.

Additional details and impacted files

[](https://app.codecov.io/gh/ianlewis/todos/pull/1464?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ian+Lewis) ```diff @@ Coverage Diff @@ ## main #1464 +/- ## ========================================== + Coverage 79.04% 79.16% +0.11% ========================================== Files 15 15 Lines 902 907 +5 ========================================== + Hits 713 718 +5 Misses 138 138 Partials 51 51 ``` | [Files](https://app.codecov.io/gh/ianlewis/todos/pull/1464?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ian+Lewis) | Coverage Δ | | |---|---|---| | [internal/cmd/todos/app.go](https://app.codecov.io/gh/ianlewis/todos/pull/1464?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ian+Lewis#diff-aW50ZXJuYWwvY21kL3RvZG9zL2FwcC5nbw==) | `85.77% <100.00%> (+0.33%)` | :arrow_up: |