⬆️ 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] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
 
     steps:
       - name: Clone repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Add symlink dir to PATH
         run: echo "$HOME/.local/bin" >> $GITHUB_PATH

.github/workflows/lint.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Clone repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Hack for setup-python cache # https://github.com/actions/setup-python/issues/807
         run: touch requirements.txt
@@ -51,7 +51,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Clone repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Link Checker
         id: lychee

.github/workflows/update-versions.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Clone repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Check if Julia is already available in the PATH
         id: julia_in_path