Wait an event loop turn in binary download test

[alfonso-noriega]

WHY are these changes introduced?

No issue; test reliability maintenance.

The binary download concurrency test now avoids fixed sleeps on main, but it still uses a bare microtask flush before asserting that the second download remains blocked. Waiting for an explicit event-loop turn better matches the async filesystem boundary the test is exercising.

WHAT is this pull request doing?

Adds a small waitForNextEventLoopTurn test helper and uses it before asserting the second binary download has not resolved while the first download is still blocked.

How to test your changes?

• pnpm test packages/app/src/cli/services/function/binaries.test.ts
• pnpm --filter @shopify/app lint
• pnpm --filter @shopify/app type-check

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