build: bump actions/checkout from 5 to 6

Author: fcharlie

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
       matrix:
         target: [win64, arm64]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 1
       - name: compile-Privexec