⬆️ Bump actions/checkout from 5 to 6 (#433)

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

Author: dependabot[bot]

.github/workflows/cache.yml

@@ -8,7 +8,7 @@ jobs:
   cache:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup Anaconda
         uses: conda-incubator/setup-miniconda@v3
         with:

.github/workflows/ci.yml

@@ -4,7 +4,7 @@ jobs:
   preview:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0  # Fetch full git history for changelog feature
       - name: Setup Anaconda

.github/workflows/execution-linux.yml

@@ -14,7 +14,7 @@ jobs:
         python-version: ["3.13"]
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - uses: conda-incubator/setup-miniconda@v3
         with:
           auto-update-conda: true

.github/workflows/execution-osx.yml

@@ -14,7 +14,7 @@ jobs:
         python-version: ["3.13"]
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - uses: conda-incubator/setup-miniconda@v3
         with:
           auto-update-conda: true

.github/workflows/execution-win.yml

@@ -14,7 +14,7 @@ jobs:
         python-version: ["3.13"]
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - uses: conda-incubator/setup-miniconda@v3
         with:
           auto-update-conda: true

.github/workflows/linkcheck.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       # Checkout the live site (html)
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: gh-pages
       - name: AI-Powered Link Checker

.github/workflows/publish.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0  # Fetch full git history for changelog feature
       - name: Setup Anaconda