Add smoke test GitHub workflow

The smoke test was broken. Putting it in a workflow ensures we find out
early if it happens again.

.github/workflows/smoke.yml

@@ -0,0 +1,16 @@
+name: Smoke Test
+on: [push, pull_request]
+jobs:
+  smoke:
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: ['2.6', '2.7', '3.0', '3.1', '3.2', head]
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - run: bundle exec ruby smoke/smoke.rb