ci: add GitHub token permissions for workflow

[varunsh-coder]

This PR adds minimum token permissions for the GITHUB_TOKEN in GitHub Actions workflows using https://github.com/step-security/secure-workflows.

Other workflows already had permissions defined.

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.

Before the change:
GITHUB_TOKEN has write permissions for multiple scopes, e.g.
https://github.com/cockroachdb/cockroach/runs/7616637964?check_suite_focus=true#step:1:19

After the change:
GITHUB_TOKEN will have minimum permissions needed for the jobs.

Signed-off-by: Varun Sharma varunsh@stepsecurity.io

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[varunsh-coder]

After reviewing previous commits for GitHub Actions workflows, I have added Release note: None to commit message.