Only run mac package tests per commit, run all platforms nightly. (#3840)

.yamato/com.unity.ml-agents-test.yml

   {% endfor %}
   triggers:
     cancel_old_ci: true
+    recurring:
+      - branch: master
+        frequency: daily
 
 {% for editor in test_editors %}
   {% for platform in test_platforms %}
     - .yamato/com.unity.ml-agents-pack.yml#pack
   triggers:
     cancel_old_ci: true
+    {% if platform.name == "mac" %}
+    {% endif %}
   {% endfor %}
 {% endfor %}