CI: Update GitHub token permissions for templates workflow

[kurmiashish]

Description

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

The GitHub Actions workflow has a GITHUB_TOKEN with write access to multiple scopes.
Here is an example of the permissions in one of the workflow runs:
https://github.com/GoogleForCreators/web-stories-wp/runs/8188010407?check_suite_focus=true#step:1:19

After this change, the scopes will be reduced to the minimum needed for the following workflow:

• update-templates.yml

The following workflow files already have the least privileged token permission set:

• add-milestone.yml
• codeql-analysis.yml
• lint-i18n.yml
• plugin-release.yml
• tests-karma-dashboard.yml
• tests-unit-php.yml
• update-product-schema.yml
• build-and-deploy.yml
• deploy-storybook.yml
• lint-php.yml
• scorecards.yml
• tests-karma-editor.yml
• update-browserslist.yml
• cleanup-pr-assets.yml
• lint-css-js-md.yml
• npm-release.yml
• tests-e2e.yml
• tests-unit-js.yml
• update-google-fonts.yml

Motivation and Context

• This is a security best practice, so if the GITHUB_TOKEN is compromised due to a vulnerability or compromised Action, the damage will be reduced.
• GitHub recommends defining minimum GITHUB_TOKEN permissions.
  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 also treats not setting token permissions as a high-risk issue. This change will help increase the Scorecard score for this repository.

Signed-off-by: Ashish Kurmi akurmi@stepsecurity.io

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