test: Introduce XS CI workflow

.github/workflows/ci.yml

@@ -260,3 +260,49 @@ jobs:
       # when imported in an NPM node_modules tree.
       - name: Prepack packages
         run: yarn lerna run --reject-cycles --concurrency 1 prepack
+
+  test-xs:
+    name: test-xs
+
+    # begin macro
+
+    runs-on: ${{ matrix.platform }}
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version: [20.x]
+        xs-version: [5.0.0]
+        platform: [ubuntu-latest]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      # without this, setup-node errors on mismatched yarn versions
+      - run: corepack enable
+
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: yarn
+
+      - name: Install dependencies
+        run: yarn install --immutable
+
+      # end macro
+
+      - name: Clone XS
+        run: git clone https://github.com/moddable-OpenSource/moddable --branch "${{ matrix.xs-version }}" --depth 1
+
+      - name: Build XS
+        working-directory: moddable/build/makefiles/lin
+        env:
+          MODDABLE: ${{ env.GITHUB_WORKSPACE }}/moddable
+        run: make
+
+      - name: Run yarn build
+        run: yarn build
+
+      - name: Run XS tests
+        run: yarn lerna run test:xs