test/mocklibc: fix build against
polkit> ../subprojects/mocklibc-1.0/src/netgroup-debug.c: In function 'netgroup_debug_print_entry':
polkit> ../subprojects/mocklibc-1.0/src/netgroup-debug.c:25:3: error: implicit declaration of function 'print_indent' [-Wimplicit-function-declaration]
polkit> 25 | print_indent(stream, indent);
polkit> | ^~~~~~~~~~~~