Reset install-classic actions/checkout to @v1

Author: rwgk

.github/workflows/ci.yml

@@ -778,7 +778,7 @@ jobs:
     timeout-minutes: 90
 
     steps:
-    - uses: actions/checkout@v6  # v1 is required to run inside docker
+    - uses: actions/checkout@v1  # v1 is required to run inside docker
 
     - name: Install requirements
       run: |