Update CA certificates and apt repositories.

The image being run while preparing the OpenZGY build, specifically while cloning seismic-store-cpp-lib, is too old with respect to the CA certificates it contains. The CA authority that signed community.opengroup.org is not recognized.

It is unclear how to update that image. Instead, this commit makes the script update ca-certificate on each run.

Note that this will only work if running as root in a container created just to run this build. Apparently this is the case. In a shared runner it would not be allowed to modify the system.

Also fixed a few unrelated problems with missing "apt-get update".