roles/icinga2: update to php7.4

roles/icinga2/templates/icinga.conf

@@ -5,7 +5,7 @@
       rewrite ^/$ icingaweb2 redirect;
     }
     location ~ ^/icingaweb2/index\.php(.*)$ {
-      fastcgi_pass unix:/var/run/php/php7.3-fpm.sock;
+      fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
       fastcgi_index index.php;
       include fastcgi_params;
       fastcgi_param SCRIPT_FILENAME /usr/share/icingaweb2/public/index.php;