update live.tests.yml and ci.tests.yml pas image when not mac, but vmImage when mac

Author: scbedd

eng/pipelines/templates/jobs/live.tests.yml

@@ -84,7 +84,12 @@ jobs:
 
     pool:
       name: $(Pool)
-      vmImage: $(OSVmImage)
+      # 1es pipeline templates converts `image` to demands: ImageOverride under the hood
+      # which is incompatible with image selection in the default non-1es hosted pools
+      ${{ if eq(parameters.OSName, 'macOS' }}:
+        vmImage: $(OSVmImage)
+      ${{ else }}:
+        image: $(OSVmImage)
       os: ${{ parameters.OSName }}
 
     ${{ if eq(parameters.UsePlatformContainer, 'true') }}: