REGTESTS: disable the test balance/balance-hash-maxqueue

This test brought by commit 8ed1e91efd ("MEDIUM: lb-chash: add directive
hash-preserve-affinity") seems to have hit a limitation of what can be
expressed in vtc, as it would be desirable to have one server response
release two clients at once but the various attempts using barriers
have failed so far. The test seems to work fine locally but still fails
almost 100% of the time on the CI, so it remains timing dependent in
some ways. Tests have been done with nbthread 1, pool-idle-shared off,
http-reuse never (since always fails locally) etc but to no avail. Let's
just mark it broken in case we later figure another way to fix it. It's
still usable locally most of the time, though.

reg-tests/balance/balance-hash-maxqueue.vtc

@@ -1,6 +1,13 @@
 
 vtest "Test for balance URI with hash-preserve-affinity maxqueue"
 feature ignore_unknown_macro
+#REGTEST_TYPE=broken
+
+# Marked as broken because despite the barriers, we're still bound by how
+# connections are established on the servers, and while it often works fine
+# locally, it tends to fail a lot on the CI. Some tests with pool-idle-shared,
+# nbthread and http-reuse never didn't help.
+
 
 # The test proceeds as follows:
 #