security: add permissions block to workflows

[elastic-vault-github-plugin-prod]

Details

⚠️ This PR was created by an automated tool. Please review the changes carefully. ⚠️

We want to set the default permissions for workflows to read-only for contents.
This is a security measure to prevent accidental changes to the repository.

This change adds a top-level permissions block to all workflows in the .github/workflows directory.

permissions:
  contents: read

In some cases workflows might need more permissions than just contents: read.
Please checkout this branch and add the necessary permissions to the workflows.

If your workflow uses a Personal Access Token (PAT), we can still add the permissions block,
but it will not have any effect.

Merging this PR as is might cause workflows that need more permissions to fail.

If there are any questions, please reach out to the @elastic/observablt-ci

[github-actions]

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[mallendem]

@copilot resolve the merge conflicts in this pull request

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[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved the merge conflict in .github/workflows/test-reporter.yml. The conflict was in the top-level permissions block — our branch had only contents: read and actions: read, while origin/main added checks: write and pull-requests: write (and removed the redundant per-job permissions from the coverage job). The file now matches origin/main (commit resolve merge conflict in test-reporter.yml with origin/main).

[github-actions]

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