using more recent bokken image for ios builds

Author: LPLafontaineB

.yamato/mobile-build-and-run.yml

@@ -9,7 +9,7 @@ Build_Player_With_Tests_iOS_{{ project.name }}_{{ editor }}:
     name: build {{ project.name }} - {{ editor }} on iOS
     agent:
         type: Unity::VM::osx
-        image: mobile/macos-10.15-testing:stable
+        image: package-ci/macos-12:v4
         flavor: b1.large
 
     commands: