place registry pidfiles inside root registry directory

Author: IanButterworth

src/Registry/Registry.jl

@@ -394,7 +394,7 @@ function update(regs::Vector{RegistrySpec} = RegistrySpec[]; io::IO=stderr_f(),
     for reg in unique(r -> r.uuid, find_installed_registries(io, regs); seen=Set{UUID}())
         let reg=reg, errors=errors
             regpath = pathrepr(reg.path)
-            Pidfile.mkpidlock(joinpath(dirname(reg.path), ".pidlock")) do # only allow one julia process to update a given registry at a time
+            Pidfile.mkpidlock(joinpath(dirname(dirname(reg.path)), ".$(reg.name).pidlock")) do # only allow one julia process to update a registry at a time
                 let regpath=regpath
                 if reg.tree_info !== nothing
                     printpkgstyle(io, :Updating, "registry at " * regpath)