[CI] restore checkout step

Author: CSY-ModelCloud

.github/workflows/compatibility.yml

@@ -15,6 +15,7 @@ jobs:
     outputs:
       versions: ${{ steps.parser.outputs.versions || '[]' }}
     steps:
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.14"

.github/workflows/unit_tests.yml

@@ -88,6 +88,7 @@ jobs:
     outputs:
       versions: ${{ steps.parser.outputs.versions || '[]' }}
     steps:
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.14"