ci: upgrade actions/checkout@v4 in github actions

Author: javier-godoy

.github/workflows/maven.yml

@@ -19,7 +19,7 @@ jobs:
   build-vaadin23:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up JDK
       uses: actions/setup-java@v3
       with:
@@ -32,12 +32,12 @@ jobs:
   build-vaadin24:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up JDK
       uses: actions/setup-java@v3
       with:
         java-version: '17'
         distribution: 'temurin'
         cache: maven
     - name: Build (Vaadin 24)
-      run: mvn -B package --file pom.xml -Pv24
+      run: mvn -B package --file pom.xml -Pv24