Bump actions/checkout from 2 to 2.3.4 (#42)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 2.3.4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v2.3.4)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
         os: [macOS-latest, windows-latest, ubuntu-latest]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
 
       - name: Use Node.js
         uses: actions/setup-node@v2.1.5