Bump actions/checkout from 2 to 4

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] <support@github.com>

.github/workflows/CICD.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
     - name: Checkout source code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Install rust toolchain
       uses: actions-rs/toolchain@v1
       with:
@@ -45,7 +45,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
     - name: Checkout source code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Install rust toolchain (v${{ env.MIN_SUPPORTED_RUST_VERSION }})
       uses: actions-rs/toolchain@v1
@@ -86,7 +86,7 @@ jobs:
           - { os: windows-2019, target: x86_64-pc-windows-msvc      }
     steps:
     - name: Checkout source code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Install prerequisites
       shell: bash