Bump actions/checkout from 5 to 6 (#274)

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

Author: dependabot[bot]

.github/workflows/auto_publish_release.yml

@@ -22,7 +22,7 @@ jobs:
     steps:
 
     - name: Checkout repo
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         ref: ${{ env.MERGE_SHA }}
 

.github/workflows/build.yml

@@ -35,7 +35,7 @@ jobs:
     name: ${{ matrix.os }} py-${{ matrix.python }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Python
         uses: mamba-org/setup-micromamba@v2

.github/workflows/create_release_pr.yml

@@ -21,7 +21,7 @@ jobs:
       uses: cylc/release-actions/stage-1/sanitize-inputs@v1
 
     - name: Checkout repo
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         ref: ${{ env.BASE_REF }}
 

.github/workflows/test.yml

@@ -43,7 +43,7 @@ jobs:
       PYTEST_ADDOPTS: -n 5 -m 'slow or not slow' --color=yes
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Python
         uses: actions/setup-python@v6
@@ -87,7 +87,7 @@ jobs:
     timeout-minutes: 2
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Download coverage artifacts
         uses: actions/download-artifact@v6

.github/workflows/update_copyright.yml

@@ -12,7 +12,7 @@ jobs:
     timeout-minutes: 10
     steps:
     - name: Checkout repo
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Configure git
       uses: cylc/release-actions/configure-git@v1