fix(deps): update pnpm/action-setup@v3 (#1477)

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## PR Checklist

- [x] Addresses an existing open issue: fixes #1487 
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/TypeStat/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/TypeStat/blob/main/.github/CONTRIBUTING.md)
were taken 🐶

## Overview

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~~I'm trying to see, will this fix inconsistency between local and CI
lint run~~

This just updates the action version. The inconsistency was because of
unrelated reason, see #1478

Co-authored-by: rubiesonthesky <rubiesonthesky>

.github/actions/prepare/action.yml

@@ -4,7 +4,7 @@ name: Prepare
 
 runs:
   steps:
-    - uses: pnpm/action-setup@v2
+    - uses: pnpm/action-setup@v3
     - uses: actions/setup-node@v4
       with:
         cache: pnpm