nginx ispconfig.vhost/apps.vhost http2 parameter incorrect behavior after update

short description

After 21db72aa ispconfig.vhost (and apps.vhost) listen directives have http2 parameter even without SSL enabled: ERR_INVALID_RESPONSE in browser after update ISPConfig.

Reproducible using nginx proxy redirect feature to access interface and apps (no need to enable SSL internally).

correct behaviour

The parameter can be added only with SSL enabled (optional in nginx_apps.vhost.master and nginx_ispconfig.vhost.master).

environment

Server OS: debian Server OS version: buster ISPConfig version: 3.2.3

If it might be related to the problem

nginx version: nginx/1.14.2

log entries

2021/03/26 11:39:16 [error] 16210#16210: *60614 upstream sent no valid HTTP/1.0 header while reading response header from upstream, client: ***, server: ***, request: "GET / HTTP/2.0", upstream: "http://127.0.0.1:8080/", host: "***"