chore(deps): update actions/checkout action to v6 (#641)

Author: renovate-bot

.github/workflows/release.yml

@@ -10,7 +10,7 @@ jobs:
     name: Run googleapis/google-cloud-php tests against latest version
     if: github.event.pull_request.user.login == 'release-please[bot]'
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Clone googleapis/google-cloud-php
       uses: actions/checkout@master
       with:

.github/workflows/tests.yml

@@ -15,7 +15,7 @@ jobs:
         runs-on: ${{ matrix.os }}
         name: PHP ${{ matrix.php }} Unit Test${{ matrix.os == 'windows-latest' && ' on Windows' || '' }}
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
             - name: Setup PHP
               uses: shivammathur/setup-php@v2
               with:
@@ -33,7 +33,7 @@ jobs:
         runs-on: ubuntu-latest
         name: Test Prefer Lowest
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
             - name: Setup PHP
               uses: shivammathur/setup-php@v2
               with: