Investigate mismatched/incompatible pointer type warnings

[bkaestner]

See the recent build log:

/home/runner/work/flux-compose/flux-compose/lib/mesche/src/object.c: In function ‘mesche_object_make_closure’:
/home/runner/work/flux-compose/flux-compose/lib/mesche/src/object.c:9:3: warning: initialization of ‘ObjectUpvalue **’ {aka ‘struct ObjectUpvalue **’} from incompatible pointer type ‘ObjectUpvalue *’ {aka ‘struct ObjectUpvalue *’} [-Wincompatible-pointer-types]
    9 |   (type)mesche_mem_realloc(NULL, 0, sizeof(type) * count)

ALLOC seems to be missing a star in the typecast. Luckily, there is only one call of ALLOC, and type is a pointer type there.