PHP 8 compatibility

The extension is not compatible with PHP 8:

```
PHP Runtime Deprecation Notice: unserialize(): Passing null to parameter #1 ($data) of type string is deprecated in /.../typo3conf/ext/phpmyadmin/ext_tables.php line 21
```

There might be more problems than the one mentioned above. Is there a timeline when the extension will be compatible with PHP 8?