Update actions/checkout action to v6 (#377)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/audit.yml

@@ -12,7 +12,7 @@ jobs:
       run:
         working-directory: ./api
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo install cargo-audit --locked
       - run: cargo audit

.github/workflows/workflow.yml

@@ -17,7 +17,7 @@ jobs:
     env:
       TZ: Europe/Amsterdam
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 24
@@ -32,7 +32,7 @@ jobs:
       run:
         working-directory: ./api
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: cargo build --verbose
       - run: cargo test --verbose
       - run: cargo clippy --verbose -- -D warnings
@@ -42,7 +42,7 @@ jobs:
     needs: [build-rs, build-ng]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: |
           REF_NAME="${{ github.ref_name }}"          
           REF_NAME_LOWER=$(echo "$REF_NAME" | tr '[:upper:]' '[:lower:]')