Singular.jl 0.18.3 released

Today Singular.jl 0.18.3 has been released.

Diff since v0.18.2

Merged pull requests:

• Convert many doc examples to doctest (#633) (@fingolfin)
• Update Singular.jl maintainers list (#634) (@fingolfin)
• Clean up docs/Project.toml (#635) (@fingolfin)
• Add gen(::sideal,::Int), gen(::FreeMod,::Int) (#636) (@fingolfin)
• Update OscarCI tests to use Julia 1.8 (#637) (@fingolfin)
• Run doctests with 1.8 (#642) (@thofma)
• Allow recent AA/Nemo versions (#646) (@thofma)