Merge branch 'sh-unset-stubenv' into 'master'

Reset the state of StubENV's @env_already_stubbed after each spec run

See merge request !12438

spec/support/stub_env.rb

@@ -5,3 +5,11 @@ module StubENV
     allow(ENV).to receive(:[]).with(key).and_return(value)
   end
 end
+
+# It's possible that the state of the class variables are not reset across
+# test runs.
+RSpec.configure do |config|
+  config.after(:each) do
+    @env_already_stubbed = nil
+  end
+end