a11y: Change button and link role

[krvpb024]

Do you follow the guidelines?

• I have tested my changes
• I read this document: https://miniflux.app/faq.html#pull-request

Made this change according to WAI-ARIA link role.

An interactive reference to an internal or external resource that, when activated, causes the user agent to navigate to that resource.
...
If pressing the link triggers an action but does not change browser focus or page location, authors are advised to consider using the button role instead of the link role.