ci: run build and test on all three platforms

Author: kermanx

.github/workflows/ci.yml

@@ -88,10 +88,12 @@ jobs:
           RUST_BACKTRACE: 1
 
   test262:
-    name: Test262
-    # TODO: Run CI on all three platforms.
-    runs-on: ubuntu-latest
+    name: Test262 (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
     timeout-minutes: 50
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
       - uses: actions/checkout@v4
       - name: Install Rust toolchain