Borg takes forever to upgrade

[HiPhish]

Hello everyone,

I was trying to upgrade my packages and Borg (the backup program) has been
taking over an hour already. I have eventually decided to cancel the upgrade
process and tried upgrading all packages except Borg. The upgrade process
finished without problems in a reasonable amount of time, so it is definitely
Borg where things get stuck.

I'm running Guix version 8cc3983a4d02a15ad4a863671c1a5a8b2b542625 after
having run `guix pull` today. Here is the output of top:

    $ top -u guixbuilder01

    top - 21:11:24 up  8:53,  4 users,  load average: 1.24, 1.54, 1.36
    Tasks: 252 total,   2 running, 189 sleeping,   0 stopped,   0 zombie
    %Cpu(s): 30.3 us,  4.4 sy,  0.0 ni, 63.0 id,  2.1 wa,  0.0 hi,  0.2 si,  
0.0 st
    KiB Mem :  6094692 total,   324704 free,  3076416 used,  2693572 buff/cache
    KiB Swap:  2097148 total,  2088176 free,     8972 used.  2595796 avail Mem 

      PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND 
                                                     
    28132 guixbui+  20   0  272972 264756  12804 R 100.0  4.3 118:56.74 
.py.test-real                                                
     4312 guixbui+  20   0   49068  29268  11508 S   0.0  0.5   0:00.61 python  
                                                     
    27994 guixbui+  20   0  132792  18296   9452 S   0.0  0.3   0:00.18 guile

Does anyone have an idea of what is going on here?