Update GitHub Action workflows to actions/checkout@v6 (8.4)

Author: TimWolla

.github/workflows/docs.yml

@@ -17,7 +17,7 @@ jobs:
     if: github.repository == 'php/php-src'
     steps:
       - name: git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install dependencies
         run: pip install sphinx-design sphinxawesome-theme rstfmt
       - name: Check formatting

.github/workflows/push.yml

@@ -48,7 +48,7 @@ jobs:
       image: 'alpine:3.22'
     steps:
       - name: git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: apk
         uses: ./.github/actions/apk
       - name: System info