Add CI workflow (#1)

Author: mattt

.github/workflows/ci.yml

@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  test:
+    name: Swift ${{ matrix.swift }} on Xcode ${{ matrix.xcode }}
+    runs-on: ${{ matrix.runs-on }}
+    env:
+      DEVELOPER_DIR: "/Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer"
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - swift: "6.0"
+            xcode: "16.0"
+            runs-on: macos-15
+          - swift: "6.1"
+            xcode: "16.3"
+            runs-on: macos-15
+          - swift: "6.2"
+            xcode: "26.0"
+            runs-on: macos-26
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build
+        run: swift build -v
+
+      - name: Test
+        run: swift test -v