bug#26975: Frequent errors in guix publish on Hydra

[Mark H Weaver]

Here's a recent excerpt of the console output from guix publish running
Hydra.  Is this expected?

      Mark

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GET /ggy44sk2w47j0dpbghpb9ipr6kik6vsm.narinfo
GET /qnpsdhgiabvr89i9vdcmhzkggs79i0pc.narinfo
GET /zgzvzsbhvyinb3vdsgswkqh2b0ih9x1i.narinfo
In guix/workers.scm:
     72:9  2 (_)
    76:32  1 (_ system-error "stat" "~A: ~S" ("No such file or d?" ?) ?)
In unknown file:
           0 (make-stack #t)
ERROR: In procedure make-stack:
ERROR: In procedure stat: No such file or directory: 
"/var/cache/guix/publish/none/zgzvzsbhvyinb3vdsgswkqh2b0ih9x1i-xclip-0.12.tar.gz.nar"
GET /j4nir8h5daijxm87gg0cr3nj9dj9fp3k.narinfo
GET /i21ndg25wzhzrb47c111jd8jv2x1sg4q.narinfo
GET /hhn63pw8s2zfawssks33q16vmv8v70y7.narinfo
In guix/workers.scm:
     72:9  2 (_)
    76:32  1 (_ system-error "stat" "~A: ~S" ("No such file or d?" ?) ?)
In unknown file:
           0 (make-stack #t)
ERROR: In procedure make-stack:
ERROR: In procedure stat: No such file or directory: 
"/var/cache/guix/publish/none/hhn63pw8s2zfawssks33q16vmv8v70y7-password-store-1.7.1.tar.xz.nar"
GET /48s10m3wwncvc441fvg4gjj8755fxdnv.narinfo
In guix/workers.scm:
     72:9  2 (_)
    76:32  1 (_ system-error "stat" "~A: ~S" ("No such file or d?" ?) ?)
In unknown file:
           0 (make-stack #t)
ERROR: In procedure make-stack:
ERROR: In procedure stat: No such file or directory: 
"/var/cache/guix/publish/none/48s10m3wwncvc441fvg4gjj8755fxdnv-qrencode-3.4.4.tar.gz.nar"
GET /3symsyfzx50zf5m2sjiszz52zbkmjrvi.narinfo
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