Fix flaky tests and improve the main workflow

[gonzaloriestra]

WHY are these changes introduced?

There are some flaky tests:

• https://github.com/Shopify/cli/actions/runs/23556199440/job/68583546608
• https://github.com/Shopify/cli/actions/runs/23556883877/job/68586009311

Also, the main checks are more unstable than the PR ones.

WHAT is this pull request doing?

• build.test.ts: downloadBinary from ./binaries.js was never mocked, causing real HTTP requests to download WASM binaries on CI. Added a partial mock to stub it as a no-op.
• http-reverse-proxy.test.ts: server.listen() calls were not awaited, so target servers could be unreachable when the proxy forwards the first request. The proxy's error handler logged warnings but never responded to the client, hanging fetch() forever. Wrapped all listen()/close() calls in promises.
• tests-main.yml: Added --pool forks on macOS to match tests-pr.yml, preventing thread-level resource contention that contributed to flakiness only on main.

How to test your changes?

CI

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	82.26%	14923/18141
🟡	Branches	74.74%	7356/9842
🟢	Functions	81.37%	3774/4638
🟢	Lines	82.64%	14109/17072

Test suite run success

3929 tests passing in 1512 suites.

Report generated by 🧪jest coverage report action from da23406

[github-actions]

We detected some changes at packages/*/src and there are no updates in the .changeset.
If the changes are user-facing, run pnpm changeset add to track your changes and include them in the next release CHANGELOG.

Caution

DO NOT create changesets for features which you do not wish to be included in the public changelog of the next CLI release.

[gonzaloriestra]

Merge activity

• Mar 26, 10:45 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Mar 26, 10:45 AM UTC: @gonzaloriestra added this pull request to the GitHub merge queue with Graphite.