Bump actions/checkout from 5 to 6 in the actions group (#355)

Bumps the actions group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `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
  dependency-group: actions
...

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/testing.yml

@@ -25,7 +25,7 @@ jobs:
 
     # Install skada
     - name: Checking Out Repository  # yamllint disable-line rule:indentation
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     # Cache 'skada' datasets
     - name: Create/Restore Skada Data Cache
       id: cache-skada_datasets
@@ -63,7 +63,7 @@ jobs:
 
     # Install skada
     - name: Checking Out Repository  # yamllint disable-line rule:indentation
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     # Install Python & Packages
     - uses: actions/setup-python@v6
       with:
@@ -96,7 +96,7 @@ jobs:
 
     # Install skada
     - name: Checking Out Repository  # yamllint disable-line rule:indentation
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     # Install Python & Packages
     - uses: actions/setup-python@v6
       with:

.github/workflows/testing_dataset.yml

@@ -29,7 +29,7 @@ jobs:
 
     # Install skada
     - name: Checking Out Repository  # yamllint disable-line rule:indentation
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     # Install Python & Packages
     - uses: actions/setup-python@v6
       with: