Refresh the cache after updating metadata in the Dbafs class

[Toflar]

The cache means that currently, setting and retrieving meta data right away in the same request, does not work.
Reproducer:

$this->filesystem->setExtraMetadata($uuid, ['foobar' => 'foo']);
$item = $this->filesystem->get($uuid); // $item will not have 'foobar' data available

[Toflar]

Failing tests unrelated.

[leofeyer]

Thank you @Toflar.