Resolve "CI jobs fail due to outdated certificate"

Description

The CI builds began failing because wget could not safely connect to the libzip server for downloading as part of Sherpa's configure step. Apparently a certificate had become invalid.

I first tried to upgrade the libzip version to be downloaded to 1.8.0. This did not help. This makes sense, because wget fails already when connecting to the server.

Then I did several attempts to add updated certificates to the Docker CentOS image used for the CI. But that didn't help either (not sure why).

Finally, I decided to just pre-install libzip in the CI Docker image, such that Sherpa can use this instead of downloading and compiling its own copy of libzip. This seems to work.

The Docker CI image changes have been pushed to https://gitlab.com/sherpa-team/sherpa-docker-build and the newly built images can be found in this repo's registry.

Test Plan

Run the CI. It should work.

Closes #323 (closed)