tests: resolve through the local dnsmasq cache in CI.

23ab627 added the cache but dropped the TEST_NGINX_RESOLVER export along
with it, so nothing points the tests at 127.0.0.1 any more. Every test file
carries its own default:

    $ENV{TEST_NGINX_RESOLVER} ||= '8.8.8.8';

so nginx's resolver directive goes straight out to a public resolver and
the cache only ever serves the warm-up digs. Public resolvers do not answer
"localhost" -- RFC 6761 leaves that to the stub resolver -- which is why
t/014-bugs.t TEST 37 and t/058-tcp-socket.t TEST 4 fail with "Host not
found".

Export TEST_NGINX_RESOLVER=127.0.0.1 so queries go through the cache, move
dnsmasq to 127.0.0.1:53, and answer the names the resolver tests need from
--host-record, since --no-hosts keeps /etc/hosts out. Port 53 keeps the
resolver addressable as a bare IP, which t/087-udp-socket.t TEST 10 needs:
it passes $TEST_NGINX_RESOLVER to setpeername() with port 53.
systemd-resolved's stub listener owns 127.0.0.53:53 only, and
--bind-interfaces keeps dnsmasq off every other address.

TEST 37 exercises nginx's resolver against a name with a trailing dot, so
give it a multi-label name, trailing-dot.test., rather than the single
label it used before. The answer still comes from a real DNS server, just
a local one.

Author: u5surf

.github/workflows/build_and_test.yml

@@ -206,6 +206,7 @@ jobs:
                        --bind-interfaces \
                        --no-resolv --no-hosts \
                        --host-record=localhost,127.0.0.1,::1 \
+                       --host-record=trailing-dot.test,127.0.0.1 \
                        --server=8.8.4.4 --server=8.8.8.8 --server=1.1.1.1 \
                        --cache-size=1000 \
                        --pid-file=/tmp/dnsmasq.pid

t/014-bugs.t

@@ -884,7 +884,7 @@ ok
 --- config
     location /t {
         resolver $TEST_NGINX_RESOLVER ipv6=off;
-        set $myhost 'localhost.';
+        set $myhost 'trailing-dot.test.';
         proxy_pass http://$myhost:$TEST_NGINX_RAND_PORT_1/t;
     }
 --- request