Merge pull request #24 from AkihiroSuda/ci-macos11

CI: enable macos-11

Author: AkihiroSuda

.github/workflows/test.yml

@@ -10,7 +10,10 @@ on:
 jobs:
   integration:
     name: Integration tests
-    runs-on: macos-10.15
+    strategy:
+      matrix:
+        platform: [macos-10.15, macos-11]
+    runs-on: ${{ matrix.platform }}
     timeout-minutes: 40
     steps:
       - uses: actions/checkout@v2