Bump actions/checkout from 3 to 4 (#24)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/dart-ci.yml

@@ -16,7 +16,7 @@ jobs:
   analyze-format:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Dart
       uses: dart-lang/setup-dart@v1
@@ -36,7 +36,7 @@ jobs:
       matrix:
         sdk-version: [ stable, beta, dev, 2.19.0 ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Dart
         uses: dart-lang/setup-dart@v1
@@ -53,7 +53,7 @@ jobs:
     needs: [analyze-format, test]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Dart
         uses: dart-lang/setup-dart@v1

.github/workflows/publish.yml

@@ -12,7 +12,7 @@ jobs:
     container:
       image:  google/dart:latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Setup credentials
         run: |
           mkdir -p ~/.pub-cache