[main] (deps): Bump actions/checkout from 2 to 3 (#41984)

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] <[email protected]>

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

.github/workflows/backport.yml

@@ -39,7 +39,7 @@ jobs:
             body: backport_start_body
           });
     - name: Checkout repo
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: Run backport

.github/workflows/runtime-sync.yml

@@ -21,14 +21,14 @@ jobs:
     runs-on: windows-latest
     steps:
     - name: Checkout aspnetcore
-      uses: actions/checkout@v2.0.0
+      uses: actions/checkout@v3
       with:
         # Test this script using changes in a fork
         repository: 'dotnet/aspnetcore'
         path: aspnetcore
         ref: main
     - name: Checkout runtime
-      uses: actions/checkout@v2.0.0
+      uses: actions/checkout@v3
       with:
         # Test this script using changes in a fork
         repository: 'dotnet/runtime'