Attachments should not be impacted by the "Forbidden page name characters" parameter

When importing a MediaWiki instance if the mediawiki+xml input filter property "Forbidden page name characters" contains a dot (.), then every link to a page attachment is likely to break.

The reason is that attachments have most of the time a file extension, such as myimage.jpg. When linking to this attachment in a wiki page, we would use [[mylink>>attach:myimage.jpg]]. However, as the dot is considered as a forbidden character in a page name, the link generated during the import corresponds to [[mylink>>attach:myimagejpg]].