Disable async DNS when use_dispatch is enabled.

In the use_dispatch setup the Matter stack is expected to not spin up
threads manually, but our async DNS implementation does just that via
pthreads.  This is leading to random failures in TestInetEndpoint on
Darwin due to thread data races.

Fixes project-chip#10025

src/inet/inet.gni

@@ -33,5 +33,6 @@ declare_args() {
 declare_args() {
   # Enable async DNS.
   chip_inet_config_enable_async_dns_sockets =
-      chip_inet_config_enable_dns_resolver && chip_system_config_use_sockets
+      chip_inet_config_enable_dns_resolver && chip_system_config_use_sockets &&
+      !chip_system_config_use_dispatch
 }