Potential fix for code scanning alert no. 5: Workflow does not contain permissions

[lenucksi]

Potential fix for https://github.com/InnerSourceCommons/InnerSourcePatterns/security/code-scanning/5

To fix the problem, we should add a permissions block to the workflow file .github/workflows/book.yml. The block should be added at the workflow root (top-level, after name: and before jobs:), so the permissions apply to all jobs in the workflow. The least privilege required is contents: write so the job can push changes to the repo (required by the auto-commit step). Other permissions (such as pull-requests: write) are not required for this workflow, as it does not modify pull requests or other resources. The block should be added after the workflow name: and before the jobs: key (best practice is before any uses of the jobs).

No imports or additional methods/definitions are needed; it's a change to the workflow configuration only.

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