build(deps): 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

@@ -11,7 +11,7 @@ jobs:
     name: Validate release surface
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Check required files
         run: |

.github/workflows/docs.yml

@@ -21,7 +21,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install mdBook
         run: |

.github/workflows/quality.yml

@@ -13,7 +13,7 @@ jobs:
     name: Stub checks
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@stable
@@ -45,7 +45,7 @@ jobs:
     name: cargo-audit
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Find stub directory
         id: stub
         run: |
@@ -62,7 +62,7 @@ jobs:
     name: License consistency
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Check license trio is present
         run: |
           set -e

.github/workflows/release.yml

@@ -58,10 +58,10 @@ jobs:
           fi
 
       - name: Checkout public release surface
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Checkout private source
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: openIE-dev/joulesperbit
           token: ${{ secrets.JOULESPERBIT_READ_TOKEN }}
@@ -131,7 +131,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download all artifacts
         uses: actions/download-artifact@v4