Add support for arm64-v8a for Apple Silicon Macs

Fixes https://github.com/ReactiveCircus/android-emulator-runner/issues/145

action.yml

@@ -2,7 +2,7 @@ name: 'Android Emulator Runner'
 description: 'Installs, configures and starts an Android Emulator directly on macOS virtual machines.'
 author: 'Reactive Circus'
 branding:
-  icon: 'smartphone'  
+  icon: 'smartphone'
   color: 'green'
 inputs:
   api-level:
@@ -12,7 +12,7 @@ inputs:
     description: 'target of the system image - default, google_apis or playstore'
     default: 'default'
   arch:
-    description: 'CPU architecture of the system image - x86 or x86_64'
+    description: 'CPU architecture of the system image - x86, x86_64 or arm64-v8a'
     default: 'x86'
   profile:
     description: 'hardware profile used for creating the AVD - e.g. `Nexus 6`'
@@ -30,7 +30,7 @@ inputs:
   disable-animations:
     description: 'whether to disable animations - true or false'
     default: 'true'
-  disable-spellchecker: 
+  disable-spellchecker:
     description: Whether to disable spellchecker - `true` or `false`.
     default: 'false'
   emulator-build: