tests/check: Avoid using "bool" for the variable name
Glib 2.82 will be aliasing [1] TRUE and FALSE to the C99 definitions, which means it will be including stdbool.h
As such, having variables named "bool" causes issues since it conflicts with the symbol defined in stdbool.h
[1] https://gitlab.gnome.org/GNOME/glib/-/merge_requests/4001