添加 ppa 后ondrej/php，我尝试sudo apt-get install php7.4，但输出是
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package php7.4
E: Couldn't find any package by glob 'php7.4'
E: Couldn't find any package by regex 'php7.4'
我已经检查过，应该使用该命令安装一个软件包，但我一定是做错了什么？