github: update test.yml to be compatible with newer requirements

The test.yml file uses actions/checkout@v4, which apparently is being
deprecated; bump to @v6 (using Node.js 24) instead.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Author: H. Peter Anvin (Intel)

.github/workflows/test.yml

@@ -20,7 +20,7 @@ jobs:
           apt-get update && apt-get install -y automake perl python3 build-essential
 
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Prepare build system
         run: |