Bump actions/checkout from 2 to 3

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v2...v3)

---
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/sdk-publish-unstable.yaml

@@ -18,7 +18,7 @@ jobs:
       run:
         working-directory: ./src
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           ref: "master"
           fetch-depth: 0

.github/workflows/sdk-publish.yaml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ startsWith(github.ref, 'refs/tags/v') && github.repository == 'jellyfin/jellyfin-sdk-csharp' }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           ref: "master"
       - uses: actions/setup-dotnet@v1