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/mypy.yaml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       # Checkout the code
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: jpetrucciani/mypy-check@master
         with:
           requirements: 1.6.0

.github/workflows/release.yml

@@ -40,7 +40,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.ref_name }}
       - name: Create release archive and notes
@@ -71,7 +71,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.tag_name || github.ref_name }}
       - if: github.event_name == 'push' || github.event.inputs.publish_to_pypi