Pass build number.

.github/workflows/build.yml

@@ -1,6 +1,3 @@
-# This workflow will build a Java project with Gradle
-# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-gradle
-
 name: build
 
 on: [pull_request, push]
@@ -31,3 +28,5 @@ jobs:
         restore-keys: ${{ runner.os }}-gradle-
     - name: Build with Gradle
       run: ./gradlew build
+      env:
+        BUILD_NUMBER: ${{ github.run_number }}