Bump actions/checkout from 2 to 3

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v2...v3)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/pr.yml

@@ -5,7 +5,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - uses: cachix/install-nix-action@v16
       with:
         nix_path: nixpkgs=channel:nixos-unstable

.github/workflows/update.yml

@@ -11,7 +11,7 @@ jobs:
   update_nur:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: '0'
     - uses: cachix/install-nix-action@v16
@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: update_nur
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - uses: cachix/install-nix-action@v16
       with:
         nix_path: nixpkgs=channel:nixos-unstable