Bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

---
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/ci.yaml

@@ -36,7 +36,7 @@ jobs:
             ubuntu: 16
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Nidhugg
         id: build
         uses: docker/build-push-action@v2
@@ -58,7 +58,7 @@ jobs:
             ubuntu: 22
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Nidhugg
         id: build
         uses: docker/build-push-action@v2
@@ -74,7 +74,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Docker Image
         id: build
         uses: docker/build-push-action@v2
@@ -89,7 +89,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       # This build in particular is slow, so enable caching for this one. All
       # our temp layers do not fit in github CI cache, so we have to be
       # selective.

.github/workflows/codespell.yml

@@ -4,7 +4,7 @@ jobs:
   codespell:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: codespell-project/actions-codespell@v2
       with:
         path: src