Fix Julia 1.11.2 WorkspaceManager race condition

[fonsp]

This should fix #3114, not yet tested

I believe the issue was caused by a race condition calling schedule twice on the same task, fixed by adding yield

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="fix-workspacemanager-task-starting-race-condition")
julia> using Pluto