chore(release): set checkout step to not persist credentials

[anpa]

Description

According to https://github.com/actions/checkout/tree/master#checkout-v2:

The auth token is persisted in the local git config. This enables your scripts to run authenticated git commands. The token is removed during post-job cleanup. Set persist-credentials: false to opt-out.

semantic-release/git#196 also hints that the semantic-release step may be using the auth token set in the checkout step.

This PR sets persist-credentials: false in the checkout step so the semantic-release step can use the token from its configuration.

Checklist

• 📗 all commit messages follow the conventional commits standard
• 💅 SASS files are compiled
• ⬅️ changes are compatible with RTL direction
• ♿ changes are accessible
• 📝 changes are tested in Chrome, Firefox, Safari, Edge, and IE11
• 👍 PR is approved by @zendesk/vikings

[zd-svc-github-copenhagen-theme]

🎉 This PR is included in version 2.2.2 🎉

The release is available on GitHub release

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