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/ci.yml

@@ -18,7 +18,7 @@ jobs:
     name: Format & Lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: dtolnay/rust-toolchain@stable
         with:
@@ -40,7 +40,7 @@ jobs:
     name: Frontend (TypeScript + Build)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-node@v4
         with:
@@ -67,7 +67,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: dtolnay/rust-toolchain@stable
 
@@ -81,7 +81,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: check
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: dtolnay/rust-toolchain@stable
 
@@ -112,7 +112,7 @@ jobs:
     name: Audit sécurité
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: rustsec/audit-check@v2.0.0
         with:

.github/workflows/fuzz.yml

@@ -25,7 +25,7 @@ jobs:
           - fuzz_template
           - fuzz_traceability
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: dtolnay/rust-toolchain@nightly
 

.github/workflows/release.yml

@@ -32,7 +32,7 @@ jobs:
             target: x86_64-pc-windows-msvc
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       # --- Rust ---
       - uses: dtolnay/rust-toolchain@stable
@@ -106,7 +106,7 @@ jobs:
             os: windows-latest
             archive: zip
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: dtolnay/rust-toolchain@stable
         with: