build: add GitHub actions

.github/workflows/tests.yml

@@ -0,0 +1,24 @@
+name: Build and run tests
+
+on:
+  push:
+    branches:
+      - '*'
+  pull_request:
+    branches:
+      - '*'
+  merge_group:
+  workflow_dispatch:
+
+jobs:
+  unit-test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-java@v3
+      with:
+        distribution: 'zulu'
+        java-version: '17'
+        cache: 'gradle'
+    - run: ./gradlew assembleDebug --stacktrace
+    - run: ./gradlew test --stacktrace