Bump actions/checkout from 5 to 6 (#78)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci-cd.yml

@@ -36,7 +36,7 @@ jobs:
     timeout-minutes: 5
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: >-
@@ -108,7 +108,7 @@ jobs:
     timeout-minutes: 5
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: Cache llhttp generated files
@@ -186,7 +186,7 @@ jobs:
     continue-on-error: ${{ matrix.experimental }}
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: Setup Python ${{ matrix.pyver }}
@@ -300,7 +300,7 @@ jobs:
     needs: pre-deploy
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: Setup Python
@@ -350,7 +350,7 @@ jobs:
           qemu: s390x
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: Set up QEMU
@@ -410,7 +410,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         submodules: true
     - name: Login

.github/workflows/codeql.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Initialize CodeQL
         uses: github/codeql-action/init@v4

.github/workflows/update-pre-commit.yml

@@ -8,7 +8,7 @@ jobs:
     if: github.repository_owner == 'aiohttp'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up Python
       uses: actions/setup-python@v6
       with: