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] <[email protected]>

.github/workflows/backend-tests.yml

@@ -22,12 +22,12 @@ jobs:
           sudo apt install -y --no-install-recommends libreoffice libreoffice-pdfimport
       -
         name: Install etherpad core
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: ether/etherpad-lite
       -
         name: Checkout plugin repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: ./node_modules/__tmp
       -

.github/workflows/frontend-tests.yml

@@ -17,7 +17,7 @@ jobs:
           printf %s\\n '::set-output name=tunnel_id::${{ github.run_id }}-${{ github.run_number }}-${{ github.job }}'
       -
         name: Check out Etherpad core
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: ether/etherpad-lite
       -
@@ -32,7 +32,7 @@ jobs:
         name: Install legacy npm for correct dependency resolution
       -
         name: Check out the plugin
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: ./node_modules/__tmp
       -

.github/workflows/npmpublish.yml

@@ -22,7 +22,7 @@ jobs:
       # conflicts with this plugin's clone, etherpad-lite must be cloned and
       # moved out before this plugin's repo is cloned to $GITHUB_WORKSPACE.
       -
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: ether/etherpad-lite
           path: etherpad-lite
@@ -31,7 +31,7 @@ jobs:
       # etherpad-lite has been moved outside of $GITHUB_WORKSPACE, so it is now
       # safe to clone this plugin's repo to $GITHUB_WORKSPACE.
       -
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       # This is necessary for actions/setup-node because '..' can't be used in
       # cache-dependency-path.
       -
@@ -79,7 +79,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       -
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       -