Fix memory leak of Ractor recv_queue

Memory leak reported:

    3   miniruby                              0x104702c1c ractor_init + 164  ractor.c:460
    2   miniruby                              0x1046496a0 ruby_xmalloc + 44  gc.c:5188
    1   miniruby                              0x10464e840 rb_gc_impl_malloc + 148  default.c:8140
    0   libsystem_malloc.dylib                0x19ab3912c _malloc_zone_malloc_instrumented_or_legacy + 152

Author: peterzhu2118

ractor_sync.c

@@ -663,6 +663,10 @@ ractor_sync_mark(rb_ractor_t *r)
 static void
 ractor_sync_free(rb_ractor_t *r)
 {
+    if (r->sync.recv_queue) {
+        ractor_queue_free(r->sync.recv_queue);
+    }
+
     // maybe NULL
     if (r->sync.ports) {
         st_free_table(r->sync.ports);