Merge branch '1474-threadsanitizer-data-race-lib-dns-message-c-v9_16' into 'v9_16'

Add missing acquire memory barrier in isc_nmhandle_unref

See merge request isc-projects/bind9!3695

lib/isc/netmgr/netmgr.c

@@ -1156,6 +1156,8 @@ isc_nmhandle_unref(isc_nmhandle_t *handle) {
 	if (isc_refcount_decrement(&handle->references) > 1) {
 		return;
 	}
+	/* We need an acquire memory barrier here */
+	(void)isc_refcount_current(&handle->references);
 
 	sock = handle->sock;
 	handle->sock = NULL;