Tests: HTTP/2 tests speedup. Similar to a78eedc39484, this change disables lingering_close in those tests that depend on open connections during graceful shutdown for testing alerts. It was ensured that disabling lingering_close does not cover alerts on older versions.

--- a/h2_ssl.t
+++ b/h2_ssl.t
@@ -48,6 +48,8 @@ http {
         ssl_certificate_key localhost.key;
         ssl_certificate localhost.crt;
 
+        lingering_close off;
+
         location / { }
     }
 }