bug#62501: [3.0.9] ‘spawn’ test fails on GNU/Hurd, due to $LD_ORIGIN_PATH

On GNU/Hurd, the ‘exec’ server always sets ‘LD_ORIGIN_PATH’ in the
environment of programs it executes—see ‘do_exec’ in ‘exec/exec.c’.
Consequently, the ‘spawn’ test that checks environment variables fails:

--8<---------------cut here---------------start------------->8---
Running posix.test
UNRESOLVED: posix.test: affinity: getaffinity
UNRESOLVED: posix.test: affinity: setaffinity
FAIL: posix.test: spawn: env with #:environment and #:output - arguments: (expected-value "GNU=guile\n" actual-value "LD_ORIGIN_PATH=/gnu/store/9ln4hd7c1p7vn31wi0cf4pp8r9sy6pvw-coreutils-8.32/bin\nGNU=guile\n")
UNRESOLVED: posix.test: spawn: ls /proc/self/fd
--8<---------------cut here---------------end--------------->8---

(This is after applying a fix for <https://issues.guix.gnu.org/61095>.)

Ludo’.