Add a workflow for running the benchmark project

Author: ultraq

.github/workflows/benchmark.yml

@@ -0,0 +1,14 @@
+name: benchmark
+
+on: [workflow_dispatch]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: gradle/wrapper-validation-action@v2
+      - uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: 21
+      - run: ./gradlew benchmark