ci: timeout curl requests after 30s (#5537)

Currently, we rely on curl's default timeout when connecting to a
resource. This is problematic because the `direct-dns` and `relayed-dns`
integration tests check that a certain resource _isn't_ accessible and
this test currently waits for 5 minutes to assert that.

We can shorten this and thus every CI by passing a `--connect-timeout`
to `curl`.

See
https://github.com/firezone/firezone/actions/runs/9656570163/job/26634409843#step:6:445
for an example CI run on `main`.

scripts/tests/lib.sh

@@ -54,7 +54,7 @@ function remove_iptables_drop_rules() {
 }
 
 function client_curl_resource() {
-    client curl --fail "$1" >/dev/null
+    client curl --connect-timeout 30 --fail "$1" >/dev/null
 }
 
 function client_ping_resource() {