tests: wait for rspamd-milter.sock in ldap and internal tests

I've hit more races in these tests recently while running the test suite
on a much faster host system.

tests/internal.nix

@@ -115,6 +115,11 @@ in
       machine.wait_for_unit("multi-user.target")
       machine.wait_for_unit("dovecot.service")
 
+      # TODO put this blocking into the systemd units?
+      machine.wait_until_succeeds(
+          "set +e; timeout 1 nc -U /run/rspamd/rspamd-milter.sock < /dev/null; [ $? -eq 124 ]"
+      )
+
       # Regression test for https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/issues/205
       with subtest("mail forwarded can are locally kept"):
           # A mail sent to user2@example.com via explicit TLS is in the user1@example.com mailbox

tests/ldap.nix

@@ -128,6 +128,11 @@ in
       machine.start()
       machine.wait_for_unit("multi-user.target")
 
+      # TODO put this blocking into the systemd units?
+      machine.wait_until_succeeds(
+          "set +e; timeout 1 nc -U /run/rspamd/rspamd-milter.sock < /dev/null; [ $? -eq 124 ]"
+      )
+
       # This function retrieves the ldap table file from a postconf
       # command.
       # A key lookup is achived and the returned value is compared