UbuntuでPHPをインストールできない

## やりたいこと
デフォルトでインストールされているPHPが7.0なので、7.4に上げたい

```
$ php -v
The program 'php' can be found in the following packages:
 * php7.0-cli
 * hhvm
Ask your administrator to install one of them
```

## 事象
PHPのパッケージがaptのリストにないためアップデートできない

```
$ sudo apt -y install php7.4
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'
```

## 解決方法
add-apt-repositoryする

```
$ sudo add-apt-repository ppa:ondrej/php
 Co-installable PHP versions: PHP 5.6, PHP 7.x and most requested extensions are included. Only Supported Versions of PHP (http://php.net/supported-versions.php) for Supported Ubuntu Releases (https://wiki.ubuntu.com/Releases) are provided. Don't ask for end-of-life PHP versions or Ubuntu release, they won't be provided.

Debian oldstable and stable packages are provided as well: https://deb.sury.org/#debian-dpa

You can get more information about the packages at https://deb.sury.org

BUGS&FEATURES: This PPA now has a issue tracker:
https://deb.sury.org/#bug-reporting

CAVEATS:
1. If you are using php-gearman, you need to add ppa:ondrej/pkg-gearman
2. If you are using apache2, you are advised to add ppa:ondrej/apache2
3. If you are using nginx, you are advised to add ppa:ondrej/nginx-mainline
   or ppa:ondrej/nginx

PLEASE READ: If you like my work and want to give me a little motivation, please consider donating regularly: https://donate.sury.org/

WARNING: add-apt-repository is broken with non-UTF-8 locales, see
https://github.com/oerdnj/deb.sury.org/issues/56 for workaround:


Creating config file /etc/php/7.4/mods-available/iconv.ini with new version

Creating config file /etc/php/7.4/mods-available/pdo.ini with new version

Creating config file /etc/php/7.4/mods-available/phar.ini with new version

Creating config file /etc/php/7.4/mods-available/posix.ini with new version

Creating config file /etc/php/7.4/mods-available/shmop.ini with new version

Creating config file /etc/php/7.4/mods-available/sockets.ini with new version

Creating config file /etc/php/7.4/mods-available/sysvmsg.ini with new version

Creating config file /etc/php/7.4/mods-available/sysvsem.ini with new version

Creating config file /etc/php/7.4/mods-available/sysvshm.ini with new version

Creating config file /etc/php/7.4/mods-available/tokenizer.ini with new version
Setting up php7.4-json (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...

Creating config file /etc/php/7.4/mods-available/json.ini with new version
Setting up php7.4-opcache (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...

Creating config file /etc/php/7.4/mods-available/opcache.ini with new version
Setting up php7.4-readline (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...

Creating config file /etc/php/7.4/mods-available/readline.ini with new version
Setting up libargon2-0:amd64 (0~20161029-1+ubuntu16.04.1+deb.sury.org+1) ...
Setting up libpcre2-8-0:amd64 (10.34-7+ubuntu16.04.1+deb.sury.org+1) ...
Setting up libsodium23:amd64 (1.0.18-1+ubuntu16.04.1+deb.sury.org+1) ...
Setting up php7.4-cli (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...
update-alternatives: using /usr/bin/php7.4 to provide /usr/bin/php (php) in auto mode
update-alternatives: using /usr/bin/phar7.4 to provide /usr/bin/phar (phar) in auto mode
update-alternatives: using /usr/bin/phar.phar7.4 to provide /usr/bin/phar.phar (phar.phar) in auto mode

Creating config file /etc/php/7.4/cli/php.ini with new version
Setting up libapache2-mod-php7.4 (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...

Creating config file /etc/php/7.4/apache2/php.ini with new version
Module mpm_event disabled.
Enabling module mpm_prefork.
apache2_switch_mpm Switch to prefork
apache2_invoke: Enable module php7.4
Setting up php7.4 (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...
Processing triggers for libc-bin (2.23-0ubuntu11) ...
Processing triggers for php7.4-cli (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...
Processing triggers for libapache2-mod-php7.4 (7.4.5-1+ubuntu16.04.1+deb.sury.org+1) ...
```

## 確認

```
$ php -v
PHP 7.4.5 (cli) (built: Apr 19 2020 07:36:13) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.5, Copyright (c), by Zend Technologies
```

参考： [Unable to locate package php7.3-gd](https://stackoverflow.com/questions/57389375/unable-to-locate-package-php7-3-gd)