bug#57215: ci: Fail to evaluate Guix specification

[Mathieu Othacehe <othacehe@gnu.org>]

Hello,

Since commit 0565cde, Cuirass fails to evaluate the guix
specification. The error messages do not give any clue, for instance:
https://ci.guix.gnu.org/eval/504294/log/raw.

I tried to strace an evaluation process of the guix specification, it
ends this way:

--8<---------------cut here---------------start------------->8---
[pid 74060] write(1, "(values (value (result (((#:job-name . guix.i686-linux) (#:derivation . \"/gnu/store/ap7sixkbikfw1xib3aisbcaw6i2005m2-guix-a5f199732.drv\") (#:inputs \"/gnu/store/4mdqwn29pvjqd6hs1q842g5wzamjy3dk-module-import-compiled.drv\" \"/gnu/store/4nv9xf9qyabcw2gz9zvxlq9ymknq7wad-guix-daemon.drv\" \"/gnu/store/a6f7jk08bs6clingcw3j8kmz3cbsj6iq-guix-command.drv\" \"/gnu/store/fl7hls4j08hp45j32xjjrjc6d49qmbmy-guix-a5f199732-modules.drv\" \"/gnu/store/h9aagy9mv2bqg7b8q3k6aksi7fa20qzc-guix-manual.drv\" \"/gnu/store/iz11170b9da1i3pkjdv6314swzvzkgvk-guile-3.0.7.drv\") (#:outputs (\"out\" . \"/gnu/store/ivs9raslmb77zn0hrcza0wbv3r9lspay-guix-a5f199732\")) (#:nix-name . \"guix-a5f199732\") (#:system . \"i686-linux\") (#:max-silent-time . 3600) (#:timeout . 18000))))))\n", 737) = -1 EPIPE (Broken pipe)
[pid 74060] --- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=74060, si_uid=997} ---
[pid 74060] futex(0x7f1110e6f330, FUTEX_WAKE_PRIVATE, 2147483647) = 0
[pid 74060] write(1, "(exception (arguments system-error (value \"fport_write\") (value \"~A\") (value (\"Broken pipe\")) (value (32))) (stack (#f (\"ice-9/boot-9.scm\" 1779 13)) (raise-exception (\"ice-9/boot-9.scm\" 1684 16)) (newline (#f #f #f)) (#f (\"guix/repl.scm\" 104 8)) (with-exception-handler (\"ice-9/boot-9.scm\" 1751 10)) (with-exception-handler (\"ice-9/boot-9.scm\" 1746 15)) (#f (\"guix/repl.scm\" 125 7))))\n", 385) = -1 EPIPE (Broken pipe)
[pid 74060] --- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=74060, si_uid=997} ---
--8<---------------cut here---------------end--------------->8---

The evaluation process receives a SIGPIPE when trying to write the
evaluation result to the pipe connecting it to "cuirass register".

Thanks,

Mathieu