only one version for now

.yamato/test_versions.metafile

 # csharp_backcompat_version is used in training-int-tests to determine the
 # older package version to run the backwards compat tests against.
 test_editors:
-  - version: 2018.4
-    csharp_backcompat_version: 1.0.0
+#  - version: 2018.4
+#    csharp_backcompat_version: 1.0.0
-  - version: 2020.1
-    csharp_backcompat_version: 1.0.0
-  - version: 2020.2
-    # 2020.2 moved the AssetImporters namespace
-    # but we didn't handle this until 1.2.0
-    csharp_backcompat_version: 1.2.0
+#  - version: 2020.1
+#    csharp_backcompat_version: 1.0.0
+#  - version: 2020.2
+#    # 2020.2 moved the AssetImporters namespace
+#    # but we didn't handle this until 1.2.0
+#    csharp_backcompat_version: 1.2.0