feat: updated Node version to 20.8.0 (#957)

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## PR Checklist

- [x] Addresses an existing open issue: fixes #953
- [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

I updated the .nvmrc version to 20.8.0 as described in the issues.

Co-authored-by: Josh Goldberg <[email protected]>

Author: biplobsd

.nvmrc

@@ -1 +1 @@
-18.18.1
+20.8.0

src/steps/writing/creation/rootFiles.ts

@@ -46,7 +46,7 @@ export async function createRootFiles(options: Options) {
 				},
 			}),
 		}),
-		".nvmrc": `18.18.0\n`,
+		".nvmrc": `20.8.0\n`,
 		".prettierignore": formatIgnoreFile([
 			...(options.excludeAllContributors ? [] : [".all-contributorsrc"]),
 			...(options.excludeTests ? [] : ["coverage/"]),