Skip graphql schema check in forks

[gonzaloriestra]

WHY are these changes introduced?

The Check graphql-codegen has been run job relies on GH secrets to fetch internal schemas. GitHub does not expose secrets to workflows triggered from forks, so the job fails with auth errors on every fork PR — the same reason dependabot[bot] PRs are already skipped.

Example: #7436

WHAT is this pull request doing?

Skip the job on PRs from forks, while still running for merge_group events (where the merge queue runs from the base repo and secrets are available).

How to test your changes?

CI

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, so I've added a changelog entry with pnpm changeset add

[github-actions]

⚠️ Potential Breaking Changes Detected

This PR contains changes that may break the existing contract.

@shopify/dev_experience — this PR contains breaking changes that require coordination for the next major release. This check will remain failed until a member of the team approves the workflow run.

💬 Head to #help-dev-platform to discuss timing and plan the release.

📝 Removed Schema Fields

The following Zod schema fields were removed or their files deleted:

File	Removed Fields	Reason
packages/app/src/cli/models/extensions/specifications/type-generation.ts	value	Fields removed