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]>

Author: dependabot[bot]

.github/workflows/build_offline_docs.yml

@@ -15,7 +15,7 @@ jobs:
           - master
           - 3.6
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           ref: ${{ matrix.branch }}
 

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install dependencies
         run: |

.github/workflows/sync_class_ref.yml

@@ -22,10 +22,10 @@ jobs:
 
     steps:
       - name: Checkout the documentation repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Checkout the engine repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: 'godotengine/godot'
           # Use the appropriate branch for the documentation version.