Bump actions/checkout from 5 to 6 (#2368) [skip ci]

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/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/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 }}
           fetch-depth: 0  # need to fetch all commits to check contributors

.github/workflows/main.yml

@@ -19,7 +19,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Node
         uses: actions/setup-node@v6
@@ -75,7 +75,7 @@ jobs:
       COVERAGE: true
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Node
         uses: actions/setup-node@v6
@@ -120,7 +120,7 @@ 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/renovate_validate.yml

@@ -20,7 +20,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Node
         uses: actions/setup-node@v6

.github/workflows/shortlog.yml

@@ -16,7 +16,7 @@ jobs:
     timeout-minutes: 10
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0  # need to fetch all commits to check contributors
 

.github/workflows/update_copyright.yml

@@ -29,7 +29,7 @@ jobs:
     steps:
 
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Configure git
         uses: cylc/release-actions/configure-git@v1