Disable impeller cmake test until it is fixed (#54788)

This task is consistently failing (with 3 retries for every engine commit). There is an issue to fix the problem, but until that issue is addressed, the task is primarily wasting CI resources.

Author: flar

.ci.yaml

@@ -515,14 +515,6 @@ targets:
       - os=Mac-13|Mac-14
       - cpu=x86
 
-  - name: Mac impeller-cmake-example
-    bringup: true
-    recipe: engine_v2/engine_v2
-    timeout: 60
-    properties:
-      cpu: arm64
-      config_name: mac_impeller_cmake_example
-
   - name: Windows windows_android_aot_engine
     recipe: engine_v2/engine_v2
     timeout: 120