Please update to depend on a more recent GNOME runtime

Hi,

here is the problem:

```
$ flatpak update
Looking for updates…

Info: runtime org.gnome.Platform branch 46 is end-of-life, with reason:
   The GNOME 46 runtime is no longer supported as of April 17, 2025. Please ask your application developer to migrate to a supported platform.
Info: applications using this runtime:
   org.remmina.Remmina
```
