feat(set_cubes_cw_max_version): only apply to py3 cubes

cube_doctor/transforms/set_cubes_cw_max_version.py

@@ -27,6 +27,9 @@ class SetCubeCubicWebMaxVersion(Command):
     AUTO_MR_AUTO_MERGE = True
     TARGETS = ("cubes",)
 
+
+    base_query = "?project lgg:has_py3_tests true ."
+
     def pre_check(self, root_files):
         if "__pkginfo__.py" in root_files:
             return