tests: Avoid invalid escaping in JSON
MangoHud historically had paths like "/usr/\$LIB/..."
in its JSON
manifest, but this is not actually valid JSON, because JSON does not
define a meaning for \$
. The version of json-glib in Debian testing
(Debian 13 prereleases) implements more correct / more strict JSON
parsing, which correctly but perhaps unhelpfully diagnoses this as an
error, breaking our test's expectations when our CI runs its tests in a
recent development environment.
We were not intentionally exercising the handling of invalid JSON, so test against valid JSON here.
I've also opened https://gitlab.gnome.org/GNOME/json-glib/-/merge_requests/87 to return json-glib in non-strict mode to its previous behaviour for these strings.