Bump actions/checkout from 3 to 4

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>

Author: dependabot[bot]

.github/workflows/dart.yml

@@ -22,7 +22,7 @@ jobs:
         sdk: [ stable ]
         package: [ prometheus_client, prometheus_client_shelf ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dart-lang/setup-dart@v1
         with:
           channel: ${{ matrix.sdk }}
@@ -58,7 +58,7 @@ jobs:
         sdk: [ dev ]
         package: [ prometheus_client, prometheus_client_shelf ]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dart-lang/setup-dart@v1
         with:
           channel: ${{ matrix.sdk }}

.github/workflows/publish.yml

@@ -17,7 +17,7 @@ jobs:
     timeout-minutes: 10
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dart-lang/setup-dart@v1
         with:
           channel: stable