chore(deps): bump actions/checkout from 6 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/actionlint.yml

@@ -13,7 +13,7 @@ jobs:
   actionlint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: raven-actions/actionlint@v2
         with:
           pyflakes: false

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: mk-all-check
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Setup elan
         run: |
           curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- -y --default-toolchain none
@@ -89,7 +89,7 @@ jobs:
     name: Check references.bib format
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Install bibtool
         run: |
           sudo apt-get update
@@ -105,7 +105,7 @@ jobs:
     name: Check mk_all executed
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Setup elan
         run: |
           curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- -y
@@ -129,7 +129,7 @@ jobs:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: pandoc/actions/setup@v1
 
       - name: Download lean artifacts