Add initial super basic GHA

Author: tianon

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+
+defaults:
+  run:
+    shell: 'bash -Eeuo pipefail -x {0}'
+
+jobs:
+  test:
+    name: Smoke Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: |
+          for dir in */; do
+            docker build --pull "$dir"
+          done