Another approach to make ""mp-units:CONAN_RUN_TESTS" work correctly

.travis.yml

@@ -1,7 +1,3 @@
-env:
-  global:
-    - mp-units:CONAN_RUN_TESTS: TRUE
-
 linux: &linux
   os: linux
   dist: xenial

build.py

@@ -26,4 +26,5 @@ if __name__ == "__main__":
     builder.add_common_builds(pure_c=False)
     for settings, options, env_vars, build_requires, reference in builder.items:
         settings["compiler.cppstd"] = "20"
+        env_vars["mp-units:CONAN_RUN_TESTS"] = "True"
     builder.run()