`ember/no-ember-testing-in-module-scope` catches assigning `Ember.testing = ...` too

Not sure how important this really is. The `ember/no-ember-testing-in-module-scope` rule (the docs, the error message, etc) claims to be about reading the value and stashing it somewhere (i.e. `let testing = Ember.testing;`), but in practice it is also catching assigning to it (`Ember.testing = false`).

I agree most of the time you shouldn't do that anyway, and in the internals where that is needed it's probably fine to disable the rule, but never the less, it seems like the rule is not doing what we expected it to do, not sure if that's intentional or not?