Merge pull request #4395 from Unity-Technologies/release_2_verified-python3

Use python3 for commands.

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

   commands:
     - npm install upm-ci-utils@stable -g --registry https://artifactory.prd.cds.internal.unity3d.com/artifactory/api/npm/upm-npm
     - upm-ci package test -u {{ editor.version }} --package-path com.unity.ml-agents {{ editor.coverageOptions }}
-    - python ml-agents/tests/yamato/check_coverage_percent.py upm-ci~/test-results/ {{ editor.minCoveragePct }}
+    - python3 ml-agents/tests/yamato/check_coverage_percent.py upm-ci~/test-results/ {{ editor.minCoveragePct }}
   artifacts:
     logs:
       paths:
     image: {{ platform.image }}
     flavor: {{ platform.flavor}}
   commands:
-    - python -m pip install unity-downloader-cli --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/unity-pypi-local/simple --upgrade
+    - python3 -m pip install unity-downloader-cli --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/unity-pypi-local/simple --upgrade
-    - python ml-agents/tests/yamato/check_coverage_percent.py upm-ci~/test-results/ {{ editor.minCoveragePct }}
+    - python3 ml-agents/tests/yamato/check_coverage_percent.py upm-ci~/test-results/ {{ editor.minCoveragePct }}
   artifacts:
     logs:
       paths: