REGTESTS: make the http-check-send test require version 2.2

It causes failures when passing regtests on older releases.
diff --git a/reg-tests/checks/http-check-send.vtc b/reg-tests/checks/http-check-send.vtc
index 4e6d61f..05f09a8 100644
--- a/reg-tests/checks/http-check-send.vtc
+++ b/reg-tests/checks/http-check-send.vtc
@@ -1,5 +1,6 @@
 varnishtest "Health-checks: http-check send test"
 #REGTEST_TYPE=slow
+#REQUIRE_VERSION=2.2
 feature ignore_unknown_macro
 
 # This script tests HTTP health-checks and more particularly the "http-check