bug#38836: guix refresh: Too many open files

[Ricardo Wurmus]

I regularly run this command:

    ./pre-inst-env guix refresh -t cran,bioconductor -u

This makes a lot of HTTP requests to check for updates.  It often aborts
with this error before it can finish checking for updates of all
packages:

   guix refresh: error: open-file: Too many open files:
   "/home/rekado/.cache/guix/http/EXpQeEGkSNjRNVeWpGMNV8ENjJfhl2vugsTbrdaTshg="

--
Ricardo