Add test workflows

* Add a basic workflow not using the Gradle GH action
* Add a basic workflow using the Gradle GH action but not doing matrix
testing

Both are only run by hand

.github/workflows/gradle-basic-build.yml

@@ -0,0 +1,21 @@
+name: Build
+on: workflow_dispatch
+jobs:
+  gradle:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-java@v3
+        with:
+          java-version: 8
+          distribution: temurin
+
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+        with:
+          # Only write to the cache for builds on the 'master' branch.
+          # Builds on other branches will only read existing entries from the cache.
+          cache-read-only: ${{ github.ref != 'refs/heads/master' }}
+
+      - name: Execute Gradle build
+        run: ./gradlew build

.github/workflows/gradle-basic.yml

@@ -0,0 +1,14 @@
+name: Basic
+on: workflow_dispatch
+jobs:
+  gradle:
+    runs-on: unbuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-java@v3
+        with:
+          java-version: 8
+          distribution: temurin
+      - name: Execute Gradle build
+        run: ./gradlew build
+