[Tests] Add test for existing hidden folder missing gitignore

[gonzaloriestra]

WHY are these changes introduced?

Improves test coverage for getOrCreateHiddenShopifyFolder in @shopify/cli-kit.

WHAT is this pull request doing?

Adds a unit test to packages/cli-kit/src/public/node/hidden-folder.test.ts verifying that when the .shopify hidden directory already exists but .gitignore inside it does not, getOrCreateHiddenShopifyFolder creates the .gitignore file.

How to test your changes?

CI

Post-release steps

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 12665915907185140325 started by @gonzaloriestra

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