REGTESTS: mark the abns test as broken again

There is apparently a race in this test that would require relying on
haproxy's output to make it reliably work, but currently vtest doesn't
have this option. Let's mark it broken again to avoid polluting the CI.

This is discussed in github issue #950.
diff --git a/reg-tests/seamless-reload/abns_socket.vtc b/reg-tests/seamless-reload/abns_socket.vtc
index d6130e7..b7d6c7c 100644
--- a/reg-tests/seamless-reload/abns_socket.vtc
+++ b/reg-tests/seamless-reload/abns_socket.vtc
@@ -20,7 +20,7 @@
 # abns@ sockets are not available on freebsd
 #EXCLUDE_TARGETS=freebsd,osx,generic
 #REQUIRE_VERSION=1.8
-#REGTEST_TYPE=bug
+#REGTEST_TYPE=broken
 
 haproxy h1 -W -conf {
   global