Update to actions/checkout@v4

Closes gh-1605

.github/workflows/deploy-docs.yml

@@ -23,7 +23,7 @@ jobs:
     if: github.repository_owner == 'spring-projects'
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: docs-build
           fetch-depth: 1

.github/workflows/release-scheduler.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 1
       - name: Dispatch