Fix testing DoH server not to concatenate responses am: 549be5d7 am: 7121a994 am: 2280a049 am: 1b45c98a

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/1899142

Change-Id: If29ed2444c523868fad24917c3ee9edeae06ce03