Use specified SQLite version also for PHP < 7.4 (#32)

## Motivation for the change, related issues
The libsqlite version [specified for PHP WASM
build](https://github.com/Automattic/wordpress-playground-private/blob/e092d448c9cd0fe56cde3a5048c132b3c55b3c04/packages/php-wasm/compile/libsqlite3/Dockerfile#L16)
was not respected for PHP < 7.4. This change fixes it for all PHP
versions.

Fixes
Automattic/wordpress-playground-private#31.

## Implementation details
Originally, it seemed that for PHP < 7.4 this [needs to be done
differently](https://www.php.net/manual/en/ref.pdo-sqlite.php):

> The PDO_SQLITE PDO driver is enabled by default. To disable,
--without-pdo-sqlite[=DIR] may be used, where the optional [=DIR] is the
sqlite base install directory. As of PHP 7.4.0 [»
libsqlite](http://sqlite.org/) ≥ 3.5.0 is required. Formerly, the
bundled libsqlite could have been used instead, and was the default, if
[=DIR] has been omitted.

However, during my testing, it turned out that simply keeping
`-lsqlite3` for all PHP versions fixes the issue. I verified this for
PHP 7.0, 7.1, 7.2, and 7.3.

## Testing Instructions (or ideally a Blueprint)
Run the following command, replacing `7.0` with any desired PHP version:
```js
PHP=7.0 npx nx run php-wasm-cli:start -- -r "var_dump(PHP_VERSION); var_dump((new PDO('sqlite::memory:'))->query('select sqlite_version()')->fetch());"
```

Author: JanJakes