bug#48127: appstream-glib build tests fail

[Jack Hill]

Some (but not much) additional info: lfam on IRC [0] noticed that Gentoo 
also has a bug report of appstream-glib test failure [1].

[0] https://logs.guix.gnu.org/guix/2021-04-30.log#233351
[1] https://bugs.gentoo.org/701980
Best,
Jack