Update binary tag used in CI
Our 'default' platform changed from x86_64-centos7-gcc9-opt
to x86_64_v2-centos7-gcc10-opt
some time ago with the move to LCG100. This MR updates the binary tag used in the CI jobs to the latest default.
This gets the build and docs jobs running again, which exposed a few errors in the documentation examples. They have now been fixed.
Edited by Alex Pearce