Try to run CI with an apple arm64 target (#166)

Author: skeet70

.github/workflows/ci.yaml

@@ -47,6 +47,8 @@ jobs:
             target: aarch64-apple-ios
           - os: macos-10.15
             target: x86_64-apple-darwin # 64-bit OSX
+          - os: macos-11
+            target: aarch64-apple-darwin # 64-bit M1 OSX
           - os: windows-2019
             target: x86_64-pc-windows-msvc
     steps: