Add manually invoked GH Actions cargo build/test run.

.github/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: ci
+
+on:
+  workflow_dispatch:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: Build
+      run: cargo build --verbose
+    - name: Run tests
+      run: cargo test --verbose