fix: create eic_xl.sif artifacts in singularity jobs for eic-shell/install.py

Since we renamed this in eic-shell/install.py (https://github.com/eic/eic-shell/pull/14/files#diff-a5fa297e66b71ac1a8685caa5c37577774be2c36024ecda7abeb70bb50214d0f), users have been trying to pull eic_xl.sif (and probably failing). This PR ensures that eic_xl.sif is published as artifact.