[Tests] Remove filesystem mocks in copy-by-pattern.test.ts

[gonzaloriestra]

WHY are these changes introduced?

The test suite for copyByPattern was using extensive filesystem mocking via vi.mock('@shopify/cli-kit/node/fs'). This leads to brittle tests that assert on implementation details (which internal functions are called) rather than actual behavior (what files are created on disk).

WHAT is this pull request doing?

• Removes vi.mock('@shopify/cli-kit/node/fs') from packages/app/src/cli/services/build/steps/include-assets/copy-by-pattern.test.ts.
• Refactors all tests to use inTemporaryDirectory and real filesystem operations.
• Updates assertions to verify the presence and content of files on disk.
• Uses fileExistsSync for assertions to comply with vitest/prefer-expect-resolves linting rules.

How to test your changes?

Run the unit tests for the affected file:

pnpm --filter @shopify/app vitest run src/cli/services/build/steps/include-assets/copy-by-pattern.test.ts

Duplicate check

I searched for previous PRs with the Jules label and "Tests" in the title using git log and available memory.

• [Tests] Remove filesystem mocks in execute-operation.test.ts: This PR targeted a different service and file.
• No other PRs were found targeting this specific subsystem or file.

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 and added a changeset with pnpm changeset add (N/A for internal test refactor)

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PR created automatically by Jules for task 220001070802494390 started by @gonzaloriestra

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