Bump actions/checkout from 2.4.0 to 3.1.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.4.0 to 3.1.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2.4.0...v3.1.0)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/haskell-ci.yml

@@ -158,7 +158,7 @@ jobs:
           chmod a+x $HOME/.cabal/bin/cabal-plan
           cabal-plan --version
       - name: checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3.1.0
         with:
           path: source
       - name: initial cabal.project for sdist

.github/workflows/nix-shell.yml

@@ -12,7 +12,7 @@ jobs:
   nix-shell:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2.4.0
+    - uses: actions/checkout@v3.1.0
     - uses: cachix/install-nix-action@v17
       with:
         nix_path: nixpkgs=channel:nixos-21.11