fix: add .allcontributorsrc back to .prettierignore (#838)

## PR Checklist

- [x] Addresses an existing open issue: fixes #837
- [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

😢. #806 was perfect. But the tooling appears to not be working properly.

fyi @conrmahr - maybe we can try again in a few months?

.prettierignore

@@ -1,3 +1,4 @@
+.all-contributorsrc
 coverage*/
 lib/
 pnpm-lock.yaml

src/steps/writing/creation/rootFiles.ts

@@ -48,6 +48,7 @@ export async function createRootFiles(options: Options) {
 		}),
 		".nvmrc": `18.17.1\n`,
 		".prettierignore": formatIgnoreFile([
+			...(options.excludeContributors ? [] : [".all-contributorsrc"]),
 			...(options.excludeTests ? [] : ["coverage/"]),
 			"lib/",
 			"pnpm-lock.yaml",