Add a GitHub action to run the regression tests

These just check that the checked in copies of the jenkinsfiles don't
trigger any unexpected exceptions or syntax errors.

Author: arichardson

.github/workflows/build-and-test.yml

@@ -0,0 +1,22 @@
+name: Build
+
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v4
+      - name: Setup Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: 17
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v4
+      - name: Build with Gradle
+        run: ./gradlew build
+      - name: Test with Gradle
+        run: ./gradlew build