ci: bump actions/checkout from 4 to 6

.github/workflows/copilot-autofix.yml

@@ -14,7 +14,7 @@ jobs:
     name: Auto-fix ShellCheck warnings
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install tools
         run: sudo apt-get install -y shellcheck

.github/workflows/lint.yml

@@ -14,7 +14,7 @@ jobs:
     name: ShellCheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install ShellCheck
         run: sudo apt-get install -y shellcheck
@@ -31,7 +31,7 @@ jobs:
     name: Validate Stow Structure
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install stow
         run: sudo apt-get install -y stow
@@ -52,7 +52,7 @@ jobs:
     name: YAML Lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Lint YAML files
         uses: ibiqlik/action-yamllint@v3

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
       !contains(github.event.head_commit.message, '[ci skip]')
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0 # full history for changelog generation