bug#59987: Guix build of guix package fails due to some graph tests failing

[Andrew Patterson]

The `guix` package currently fails to build.  Looking at the build 
log, this is because some tests in tests/graph.scm fail, and the 
actual test log complains about a wrong arg type to 
scm_to_utf8_stringn for both failing tests.  I did recently have a 
transient `guix pull` issue with a similar error, but guix is now 
functioning as usual.

Both the build log and tests/graph.scm test log are attached below

txtTnFj4uMxGS.txt
Description: Build log

txtM99KFKn4lG.txt
Description: Failing tests log

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Andrew Patterson