[Devops] Install ISPC into Blender container (#21938)
Required to build Blender and its deps. We might be able to get rid of
the dependency but I'm not sure of the impact and it's a small self
contained package so IMO not worth, just include it.
It's already installed on the Windows machines which don't use Docker.
Signed-off-by: Nick Sarnie <nick.sarnie@intel.com>
