make build hangs, possible because of old version of Poetry

[OrangeTux]

The README.md instructs users to run make build. In turn, docker-compse build which builds the Dockerfile.

Building the Dockerfile never finishes. The flow hangs at Dockerfile:27.
https://github.com/SwitchEV/pyslac/blob/e047321ae437ac6fd38a6fd619096ea3131e6da7/Dockerfile#L27

While debugging this issue, I noticed that the Dockerfile is using Poetry 1.1.11. This is a very old version of Poetry.
The latest version is 1.6.x.

Updating to Poetry 1.6 prevents the hanging.