Fix PrivateDnsDohTest.ExcessDnsRequests not to interfere other tests am: a4d7bb98 am: 398b9419 am: 143a5714 am: a8ea7154

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/2005392

Change-Id: Ifcc88475f56a36052cf91dfd76fc7a15da7f145f