您只需像在本地执行一样执行Gradle。
看一下这个YAML示例：

name: Build Release APK

on:
  push:
    branch:
      - 'master'

jobs:
  Gradle:
    runs-on: ubuntu-latest
    steps:
    - name: checkout code
      uses: actions/checkout@v2
    - name: setup jdk
      uses: actions/setup-java@v1
      with:
        java-version: 11
    - name: Make Gradle executable
      run: chmod +x ./gradlew
    - name: Build Release APK
      run: ./gradlew assembleRelease

灵感：https://github.com/marketplace/actions/build-android-release-apk-when-create-new-tag