fix: correct permissions for browsertesting-open-issue workflow

[DeagleGross]

continuation for #62845, it appears that we need to set permissions on the job so that GH_TOKEN has enough rights to open the issue. see failed workflow run: https://github.com/dotnet/aspnetcore/actions/runs/16465776673/job/46542680254 and error:

Run gh issue create
gh issue create
--title "Request Browser-Testing Dependencies Update"
--body-file ".github/workflows/browsertesting-issue-body.md"
--assignee "@copilot"
shell: /usr/bin/bash -e {0}
env:
GH_TOKEN: ***
GH_REPO: dotnet/aspnetcore
GraphQL: Resource not accessible by integration (createIssue)

[Copilot]

Pull Request Overview

This PR fixes a permissions issue in the browsertesting-open-issue GitHub workflow by adding explicit job-level permissions. The workflow was previously failing with a "Resource not accessible by integration" error when attempting to create GitHub issues because the default GITHUB_TOKEN lacked sufficient permissions.

• Adds explicit permissions block to the create-issue job
• Grants contents: read and issues: write permissions to enable issue creation

[sebastienros]

Other workflows have it so I don't think it's a problem