print system time on all mac builds (#29025)

.cirrus.yml

@@ -163,6 +163,10 @@ task:
     PUBLISHING_MATCH_CERTIFICATE_REPO: git@github.com:flutter/private_publishing_certificates.git
   osx_instance:
     image: mojave-xcode-10.1
+  # occasionally the clock on these machines is out of sync
+  # with the actual time - this should help to verify
+  print_date_script:
+    - date
   git_fetch_script:
     - git clean -xfd
     - git fetch origin
@@ -182,6 +186,10 @@ task:
   env:
     CIRRUS_WORKING_DIR: "/tmp/flutter sdk"
     COCOAPODS_DISABLE_STATS: true
+  # occasionally the clock on these machines is out of sync
+  # with the actual time - this should help to verify
+  print_date_script:
+    - date
   install_cocoapods_script:
     - sudo gem install cocoapods
   git_fetch_script: