fix(ci): revert GraphQL field to closingIssuesReferences

[CasualDeveloper]

Summary

Fixes the GraphQL field name in the PR standards workflow from issuesReferences to closingIssuesReferences.

Problem

While submitting #7443, we noticed the check-standards job was failing: https://github.com/anomalyco/opencode/actions/runs/20845955619/job/59889485904?pr=7443

The error:

Field 'issuesReferences' doesn't exist on type 'PullRequest'

The correct field name in GitHub's GraphQL API is closingIssuesReferences.

Solution

Update the field name to match the GitHub GraphQL API schema.

Fixes #7446