ci: add checkout

Author: silenium-dev

.github/workflows/ffmpeg.yml

@@ -139,6 +139,7 @@ jobs:
     name: Publish Kotlin artifacts
     runs-on: ubuntu-22.04
     steps:
+      - uses: actions/checkout@v4
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v3
         with: