Singular.jl 0.18.4 released

Today Singular.jl 0.18.4 has been released.

Diff since v0.18.3

Merged pull requests:

• fix important(?) typo (#648) (@lgoettgens)
• Move test dependencies to test/Project.toml (#649) (@lgoettgens)
• CI: enable color for OscarCI diffs (#650) (@fingolfin)
• CI: use julia-actions/cache (#651) (@fingolfin)
• Add Aqua.jl for some static testing (#652) (@lgoettgens)
• detect NULL-Ptr (to avoid seg-fault) (#653) (@fieker)
• Update libsingular_julia_jll (#654) (@fingolfin)
• Remove redundant ‘using CxxWrap’ (#655) (@fingolfin)
• Track invalidations in CI, report if they increase (#656) (@lgoettgens)
• Merge libsingular-julia back into Singular.jl (#657) (@fingolfin)
• Update to latest JLL versions (#658) (@fingolfin)