build: add GitHub token permissions for workflows
This PR adds minimum token permissions for the GITHUB_TOKEN using https://github.com/step-security/secure-workflows.
GitHub recommends defining minimum GITHUB_TOKEN permissions for securing GitHub Actions workflows
- https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token/
- https://docs.github.com/en/actions/security-guides/automatic-token-authentication#modifying-the-permissions-for-the-github_token
- The Open Source Security Foundation (OpenSSF) Scorecards treats not setting token permissions as a high-risk issue
This project is part of the top 100 critical projects as per OpenSSF (https://github.com/ossf/wg-securing-critical-projects), so fixing the token permissions to improve security.
Signed-off-by: Varun Sharma varunsh@stepsecurity.io