Flagged with EOL `org.kde.Platform` 6.9 runtime warning in GNOME Software

When viewing `org.musescore.MuseScore` in GNOME Software (or during terminal updates via `flatpak update`), a **"Stopped Receiving Updates"** warning banner is displayed.

```text
lauritz@my-machine ~> flatpak update
Info: runtime org.kde.Platform branch 6.9 is end-of-life, with reason:
We strongly recommend moving to the latest stable version of the Platform and SDK
Info: applications using this runtime:
org.musescore.MuseScore
```

This warning occurs because `org.musescore.MuseScore.yaml` remains pinned to `org.kde.Platform//6.9`, which has reached end-of-life status.

### Steps to Reproduce

1. Install `org.musescore.MuseScore` from Flathub:

2. Execute a Flatpak update check:
```bash
flatpak update
```

3. Observe the CLI notice regarding `org.kde.Platform` 6.9 being end-of-life.
4. Open the MuseScore details page in GNOME Software to observe the warning banner.

### Expected Behavior

`org.musescore.MuseScore` should target an active, supported KDE Platform runtime branch (e.g., `6.10` or newer), preventing EOL warnings in the CLI and GNOME Software.

Start with org.musescore.MuseScore.yaml and inspect the org.kde.Platform runtime branch currently set to 6.9. Update it to an active supported branch, then run flatpak update and check MuseScore in GNOME Software to confirm the EOL warning is gone.

Written by the indexing model from the issue text.