Add GitHub Actions CI to ensure builds & tests succeed on Mac & Linux

Author: Jeehut

.github/workflows/main.yml

@@ -0,0 +1,23 @@
+name: CI
+
+on:
+  pull_request:
+
+jobs:
+  test-linux:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run tests
+        run: swift test
+
+  test-macos:
+    runs-on: macos-15
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run tests
+        run: swift test