ci: add GitHub Actions workflow for pull requests

Runs tests on PRs and pushes to main.

.github/workflows/test.yml

@@ -0,0 +1,25 @@
+name: Tests
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Clean vendor
+        run: rm -rf vendor
+
+      - name: Test
+        run: go test -race -v ./...