ci: test IPv6 for CIDR resources (#10168)

Docker for Mac finally supports IPv6 in general availability. It's time
to add IPv6 to our suite of integration tests.

The thinking behind this PR is try and not slow down CI much, if at all,
by testing IPv6 side-by-side with the existing IPv4 tests.

More comprehensive testing is being developed in #10131 that will test
things like IPv4-in-6 relaying, client / gateway IP stack mismatches,
and so forth.

scripts/tests/systemd/dns-systemd-resolved.sh

@@ -10,6 +10,7 @@ SERVICE_NAME=firezone-client-headless
 debug_exit() {
     echo "Bailing out. Waiting a couple seconds for things to settle..."
     sleep 5
+    docker compose ps -a
     resolvectl dns tun-firezone || true
     systemctl status "$SERVICE_NAME" || true
     exit 1

scripts/tests/systemd/env

@@ -1 +1 @@
-FIREZONE_API_URL=ws://localhost:8081
+FIREZONE_API_URL=ws://127.0.0.1:8081

scripts/tests/systemd/firezone-client-headless.service

@@ -34,7 +34,7 @@ SystemCallArchitectures=native
 SystemCallFilter=@aio @basic-io @file-system @io-event @network-io @signal @system-service
 UMask=077
 
-Environment="FIREZONE_API_URL=ws://localhost:8081"
+Environment="FIREZONE_API_URL=ws://127.0.0.1:8081"
 # TODO: Remove after #6163 gets into a release
 Environment="FIREZONE_DNS_CONTROL=systemd-resolved"
 Environment="RUST_LOG=info"