Bump actions/checkout from 3 to 4 (#57)

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/default.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Docker meta
         id: meta

.github/workflows/nightly.yml

@@ -12,7 +12,7 @@ jobs:
         java: [11]
     steps:
       - name: Checkout GitBucket repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: gitbucket/gitbucket
           path: gitbucket
@@ -34,7 +34,7 @@ jobs:
           sbt executable
 
       - name: Check out the repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: docker