fix: database as optional parameter for set_credentials (#25)

This is another follow-up PR for #22 which fixes a deprecation issue about defining optional parameters that are then called as named.

```php
Database::set_credentials("db");
```
```
vlw\Scaffold\Database::set_credentials(): Optional parameter $host declared before required parameter $database is implicitly treated as a required parameter
```

Reviewed-on: https://codeberg.org/vlw/scaffold/pulls/25

src/Database/Database.php

@@ -32,7 +32,7 @@
 			?string $host = self::DEFAULT_HOSTNAME,
 			?string $username = self::DEFAULT_USERNAME,
 			?string $password = self::DEFAULT_PASSWORD,
-			string $database
+			?string $database = ""
 		) {
 			// Create key if it does not exist
 			if (!$_ENV["mariadb"]) {