ci: Update checkout to silence Node.js messages

Github actions warnings:

  Node.js 20 actions are deprecated...

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Author: krzk

.github/workflows/ci.yml

@@ -327,7 +327,7 @@ jobs:
         echo "VARIANT: $VARIANT"
 
     - name: Git checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Install additional packages
       run: |