fix: remove .all-contributorsrc from .prettierignore (#806)

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## PR Checklist

- [x] Addresses an existing open issue: fixes #801
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/create-typescript-app/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/create-typescript-app/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

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This PR is a fix for the all-contributors/cli#347 issue now being
resolved. Ignoring the `.all-contributorsrc` file in the
`.prettierignore` file is unnecessary. 😎

Author: conrmahr