netmgr unit test fails to build with disabled DoH

The netmgr unit test from the bind-9.18 branch fails to build with disabled DoH (./configure --enable-developer --disable-doh) on Fedora 40:

netmgr_test.c: In function ‘run_test_tlsdns_server_send_many_recv_one’:
netmgr_test.c:2538:18: error: implicit declaration of function ‘isc_nm_listentls’; did you mean ‘isc_nm_listentcp’? [-Wimplicit-function-declaration]
 2538 |         result = isc_nm_listentls(
      |                  ^~~~~~~~~~~~~~~~
      |                  isc_nm_listentcp

It is likely just a missing #ifdef HAVE_LIBNGHTTP2 around the affected code.