Build the self monitor reference with term_from_ref_ticks

Monitoring self installs no alias, so the returned reference is always a
short ref. The path reserved TERM_BOXED_SHORT_REF_SIZE but built the term
with term_from_ref_data, whose allocation size depends on the embedded
pid. At runtime this is safe (process_id is INVALID_PROCESS_ID, so
term_from_ref_data returns a short ref of exactly that size), but the
static allocation check cannot prove the pid stays invalid and sizes it
as a process ref, reporting a 3-vs-2 term over-allocation.

Call term_from_ref_ticks directly: it allocates exactly
TERM_BOXED_SHORT_REF_SIZE, matching the reservation, and is identical to
what term_from_ref_data does for an invalid pid.

Signed-off-by: Davide Bettio <davide@uninstall.it>

Author: bettio

src/libAtomVM/nifs.c

@@ -5069,11 +5069,14 @@ static term nif_erlang_monitor(Context *ctx, int argc, term argv[])
         // with {alias, _}, no alias either -- sends to the returned reference are dropped,
         // unalias/1 and demonitor(Ref, [info]) return false.
         if (UNLIKELY(local_process_id == ctx->process_id)) {
-            RefData ref_data = { .ref_ticks = globalcontext_get_ref_ticks(ctx->global), .process_id = INVALID_PROCESS_ID };
             if (UNLIKELY(memory_ensure_free_opt(ctx, TERM_BOXED_SHORT_REF_SIZE, MEMORY_CAN_SHRINK) != MEMORY_GC_OK)) {
                 RAISE_ERROR(OUT_OF_MEMORY_ATOM);
             }
-            return term_from_ref_data(&ref_data, &ctx->heap);
+            // No alias is installed, so this is always a short ref. term_from_ref_ticks allocates
+            // exactly TERM_BOXED_SHORT_REF_SIZE, matching the reservation; term_from_ref_data sizes
+            // by pid, which the allocation checker can't prove stays short here.
+            uint64_t ref_ticks = globalcontext_get_ref_ticks(ctx->global);
+            return term_from_ref_ticks(ref_ticks, &ctx->heap);
         }
 
         target = globalcontext_get_process_lock(ctx->global, local_process_id);