v2.6.5 Coriander

Two changes stand out in this small release:

1. #4454 The lists of products in the OC create/edit pages are sorted alphabetically.
2. #4136 Multiple concurrent checkouts for the same variant are now waiting for each other and not reducing stock into the negative.

We also include some maintenance:

#4463 Use .ruby-version when building Docker container
#4479 Bump ddtrace from 0.28.0 to 0.29.0
#4478 Bump rspec-retry from 0.6.1 to 0.6.2
#4486 Updated translations