feat: Add initial github action

This enables a github action which simply runs all the tests, including
the slow ones.

.github/workflows/test.yml

@@ -0,0 +1,17 @@
+name: Tests
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: '>=1.20'
+      - run: make test