GAP.jl 0.8.4 released

Today GAP.jl 0.8.4 has been released.

Diff since v0.8.3

Closed issues:

• Loading GAP in parallel julia setup fails (#828)
• Print about xgap package when loading OSCAR (#831)

Merged pull requests:

• Avoid race when loading GAP.jl concurrently in multiple processes (#829) (@fingolfin)
• CI: update some actions to latest versions (#830) (@fingolfin)