ci: add GitHub token permissions for workflow

[varunsh-coder]

Summary of Changes

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 [email protected]

Testing Instructions

N/A

Actual result BEFORE applying this Pull Request

GITHUB_TOKEN has all permissions
https://github.com/joomla/joomla-cms/runs/7143497554?check_suite_focus=true#step:1:16

Expected result AFTER applying this Pull Request

GITHUB_TOKEN will have minimum permissions needed

Documentation Changes Required

N/A

[zero-24]

Looks good to me @wilsonge can you please double check here?

[wilsonge]

LGTM. I'm not adding this to the release milestone as it just affects the .github directory. But feel free to overrule

[zero-24]

Thanks will assign to 3.10 as its a action that only runs for this release.