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_proxy_cache.t
+++ b/h2_ssl_proxy_cache.t
@@ -51,6 +51,7 @@ http {
         ssl_certificate localhost.crt;
 
         send_timeout 1s;
+        lingering_close off;
 
         location / {
             proxy_pass   http://127.0.0.1:8081;