Possible fix for 2.3 not working on linux and added github action to run unit tests on linux

[doozMen]

I can imagine that the locking code I added is not the best but it works on linux. Could you if you do not agree with it add better code.

To help I added a yml file that in my fork successfully runs the unit tests on ubuntu latests (which includes swift by default).

Please let me know what I could change to make this acceptable?

References

• possible fix for #152