Bump actions/checkout from 2 to 4 (#56)

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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Setup .NET Core 2.1
@@ -52,7 +52,7 @@ jobs:
     runs-on: windows-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Setup .NET
         uses: actions/setup-dotnet@v4
       - uses: actions/download-artifact@v2
@@ -77,7 +77,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Setup .NET
@@ -96,7 +96,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Setup .NET