Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
     timeout-minutes: 10
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v4
         with:
           version: 10
@@ -41,7 +41,7 @@ jobs:
     timeout-minutes: 10
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v4
         with:
           version: 10
@@ -75,7 +75,7 @@ jobs:
           - embroider-optimized
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v4
         with:
           version: 10