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/lint.yaml

@@ -5,7 +5,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v5
         with:
           python-version: "3.10"

.github/workflows/release_to_pypi.yaml

@@ -11,7 +11,7 @@ jobs:
       contents: write
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v5
         with:

.github/workflows/tests.yaml

@@ -25,7 +25,7 @@ jobs:
             experimental: false
             coverage: true
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
       - name: Set up micromamba

.github/workflows/tests_windows.yaml

@@ -17,7 +17,7 @@ jobs:
         python-version: ["3.10", "3.11", "3.12", "3.13"]
         experimental: [false]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
       - name: Set up micromamba and install package dependencies