race condition when multiple terminals open at once, and write completer's `gh.ps1`

[ninmonkey]

Sometimes there's a race condition.

Import-Module: C:\Users\cppmo_000\Documents\2021\dotfiles_git\powershell\Nin-CurrentUserAllHosts.ps1:217
Line |
 217 |      Import-Module -Name $p -Force #-ea stop
     |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | The process cannot access the file
     | 'C:\Users\cppmo_000\.ninmonkey\completers\gh.ps1' because it is being
     | used by another process.

Resolution, either:

A) tiny sleep and retry once
B) don't recreate / write completers on all executions of profile -- read, but write once.
C) mutex on write

( multiple attempts to write are causing the problem )

Minimal mutex, so B + C in a wrapper is possibly the best route, because multiple are used.