[Tests] Replace filesystem mocks with real temp directories in bundle.test.ts

[gonzaloriestra]

WHY are these changes introduced?

Following best practices to use real temporary directories instead of mocking the filesystem in tests.

WHAT is this pull request doing?

Refactored bundleExtension tests in packages/app/src/cli/services/extensions/bundle.test.ts to use inTemporaryDirectory and readFile/fileExistsSync for assertions. Removed the global vi.mock('@shopify/cli-kit/node/fs') block.

How to test your changes?

CI

Post-release steps

None

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 7849776053424436107 started by @gonzaloriestra

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