ci: Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/benchmark.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       # ── Build Isartor ──────────────────────────────────────────────────────
       - name: Install system dependencies
@@ -162,7 +162,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Run harness in dry-run mode
         run: python3 benchmarks/run.py --all --dry-run

.github/workflows/ci.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install system dependencies
         run: |
@@ -60,7 +60,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install system dependencies
         run: |

.github/workflows/docs.yml

@@ -20,7 +20,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install mdBook
         run: |

.github/workflows/release.yml

@@ -73,7 +73,7 @@ jobs:
       PROJECT_NAME: isartor
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -224,7 +224,7 @@ jobs:
       packages: write
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Download Linux build artifacts
         uses: actions/download-artifact@v4

.github/workflows/scenario-run.yml

@@ -66,7 +66,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v5

.github/workflows/tag_release.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0