fix: default checkout-fetch-depth to shallow clone (1)

[Copilot]

This action currently defaults checkout-fetch-depth to 0, which fetches full history. This PR aligns default behavior with the issue requirement by making shallow checkout (1) the default while preserving explicit override support (0, 2, etc.).

• Default behavior update

  • Changed inputs.checkout-fetch-depth.default in action.yml from 0 to 1.

• Documentation alignment

  • Updated the README input table to reflect default checkout-fetch-depth: 1.

• Focused workflow coverage for default path

  • Updated checkout workflow coverage to exercise the default (no explicit checkout-fetch-depth in test-checkout).
  • Added a shallow-repo assertion in the checkout verification step.

# action.yml
inputs:
  checkout-fetch-depth:
    description: 'Depth of commit history to fetch'
    required: false
    default: '1'

[Copilot]

Pull request overview

This PR changes the composite action’s default repository checkout behavior to use a shallow clone (fetch depth 1) instead of fetching full history, and aligns docs/tests with that new default.

Changes:

• Updated checkout-fetch-depth default in action.yml from 0 (full history) to 1 (shallow).
• Updated README input table to reflect the new default.
• Adjusted the checkout-focused workflow to exercise the default path and assert the repo is shallow.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
action.yml	Sets checkout-fetch-depth default to shallow clone (1).
README.md	Updates documented default for checkout-fetch-depth to 1.
.github/workflows/test.yml	Removes explicit fetch-depth override in test-checkout and adds an assertion that checkout is shallow by default.

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