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/automerge.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
 
       - name: Automerge
         id: automerge

.github/workflows/backend-tests.yml

@@ -22,7 +22,7 @@ jobs:
           version: 1.0
       -
         name: Install etherpad core
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           repository: ether/etherpad-lite
           path: etherpad-lite
@@ -48,7 +48,7 @@ jobs:
             ${{ runner.os }}-pnpm-store-
       -
         name: Checkout plugin repository
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           path: plugin
       - name: Remove tests

.github/workflows/frontend-tests.yml

@@ -12,7 +12,7 @@ jobs:
     steps:
       -
         name: Check out Etherpad core
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           repository: ether/etherpad-lite
           path: etherpad-lite
@@ -38,7 +38,7 @@ jobs:
             ${{ runner.os }}-pnpm-store-
       -
         name: Checkout plugin repository
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           path: plugin
       -

.github/workflows/npmpublish.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Upgrade npm to >=11.5.1 (required for trusted publishing)
         run: npm install -g npm@latest
       - name: Check out Etherpad core
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           repository: ether/etherpad-lite
       - uses: pnpm/action-setup@v6
@@ -47,7 +47,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-pnpm-store-
       -
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
         with:
           fetch-depth: 0
       -