[ci] update actions to v4

* See deprecation notice: https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/
* Let's update all `actions` packages to v4
* The `android-actions/setup-android` is still on release v3

.github/workflows/ci.yml

@@ -8,9 +8,9 @@ jobs:
   build:
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: "[Setup] Java"
-        uses: actions/setup-java@v3
+        uses: actions/setup-java@v4
         with:
           java-version: '17'
           distribution: 'temurin'
@@ -29,7 +29,7 @@ jobs:
           ./gradlew testReleaseUnitTest --console=plain --continue
       - name: Unit tests results
         if: failure()
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: unit-tests-results
           path: OneSignalSDK/unittest/build