Try hard coding the editor path.

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

     - python3 -m pip install unity-downloader-cli --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/pypi/simple --upgrade
     - unity-downloader-cli -u trunk -c editor --wait --fast
     - 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 }}
+    - upm-ci package test -u C:\build\output\Unity-Technologies\ml-agents\.Editor --package-path com.unity.ml-agents {{ editor.coverageOptions }}
     - python3 ml-agents/tests/yamato/check_coverage_percent.py upm-ci~/test-results/ {{ editor.minCoveragePct }}
   artifacts:
     logs: