Update actions/checkout action to v6

.github/workflows/claude-code-review.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 1
 

.github/workflows/claude.yml

@@ -26,7 +26,7 @@ jobs:
       actions: read
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 1
 

.github/workflows/dotfiles.yml

@@ -11,7 +11,7 @@ jobs:
     name: Shellcheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: false  # Don't need submodules for linting our scripts
 
@@ -44,7 +44,7 @@ jobs:
     name: Syntax check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install zsh
         run: sudo apt-get install -y zsh
@@ -59,7 +59,7 @@ jobs:
     name: Verify structure
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Required config files exist
         run: |