Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

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

.github/workflows/ci-pr.yml

@@ -30,7 +30,7 @@ jobs:
 
     steps:
       - name: Checkout PR branch into cwd
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           # Checkout the fork/head-repository to push changes to the fork.
           # Without this the base repository will be checked out and committed to.
@@ -40,7 +40,7 @@ jobs:
           ref: ${{ github.head_ref }}
 
       - name: Checkout main branch into directory _main_branch/
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: main
           path: _main_branch

.github/workflows/merge.yml

@@ -31,13 +31,13 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           # Using fetch-depth 0 is the only way to get all tags which are needed for building docs.
           fetch-depth: 0
 
       - name: Checkout gh-pages branch to dir publish/
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: gh-pages
           path: publish

.github/workflows/publish.yml

@@ -31,13 +31,13 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           # Using fetch-depth 0 is the only way to get all tags which are needed for building docs.
           fetch-depth: 0
 
       - name: Checkout gh-pages branch to dir publish/
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: gh-pages
           path: publish