build(deps): bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ jobs:
   whitespace-errors:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: check
       run: git diff-index --check --cached 4b825dc642cb6eb9a060e54bf8d69288fbee4904
 
@@ -16,7 +16,7 @@ jobs:
       CC: gcc-14
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -30,7 +30,7 @@ jobs:
       CC: gcc-13
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -44,7 +44,7 @@ jobs:
       CC: gcc-12
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -58,7 +58,7 @@ jobs:
       CC: gcc-11
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -72,7 +72,7 @@ jobs:
       CC: gcc-10
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -86,7 +86,7 @@ jobs:
       CC: gcc
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -100,7 +100,7 @@ jobs:
       CC: clang-18
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -114,7 +114,7 @@ jobs:
       CC: clang-17
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -128,7 +128,7 @@ jobs:
       CC: clang-16
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -142,7 +142,7 @@ jobs:
       CC: clang-15
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -156,7 +156,7 @@ jobs:
       CC: clang-14
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -170,7 +170,7 @@ jobs:
       CC: clang-13
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -184,7 +184,7 @@ jobs:
       CC: clang-12
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -198,7 +198,7 @@ jobs:
       CC: clang-11
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies
@@ -212,7 +212,7 @@ jobs:
       CC: clang
       TARGET: x86_64
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: install dependencies