LGTM.com - false positive cpp/missing-return co-routines

**Description of the false positive**

Co-routines do not need a return statement even though it has a return value. Since the co-routine immediatly returns the return value as-if a promise.

**URL to the alert on the project page on LGTM.com**

Since LGTM.com does not recognise my project as a c++ project here is the github page: https://github.com/ttauri-project/ttauri/blob/0bf4717084fbc7d86d569b9722547884c0ac88e9/src/ttauri/ranges.hpp#L49-L49