GitHub Action: Bump actions/checkout from 3 to 4 (#690)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to
4.

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

.github/workflows/Build-UefiExt.yaml

@@ -29,7 +29,7 @@ jobs:
     runs-on: windows-2022
     steps:
       - name: Check out repository code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       
       - name: Setup MsBuild
         uses: microsoft/setup-msbuild@v1.3