Rebased spack-packages on Remote Leads to Divergent History on Gadi

[CodeGat]

See run https://github.com/ACCESS-NRI/ACCESS-OM2/actions/runs/11829981295/job/32962759210#step:8:29 - there is history divergence because of rebases on spack-packages development branches.

Instead of using git checkout --force $BRANCH, which still has the divergent branch issue, use git reset --hard origin/$BRANCH, since we only care about what is done on the remote.