Build unmerged branch on pull request

.github/workflows/build.yml

@@ -23,6 +23,10 @@ jobs:
       cancel-in-progress: true
     steps:
       - uses: actions/checkout@v3
+        with:
+          # Ensure we are building the branch and not the branch after being merged on develop
+          # https://github.com/actions/checkout/issues/881
+          ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.ref }}
       - name: Assemble debug APK
         run: ./gradlew assembleDebug $CI_GRADLE_ARG_PROPERTIES
       - name: Upload debug APKs