Flatpak runtime org.gnome.Platform branch 43 is end-of-life

[ViViDboarder]

Describe the bug
When updating Flatpaks, I get the following warning:

Info: runtime org.gnome.Platform branch 43 is end-of-life, with reason:
   The GNOME 43 runtime is no longer supported as of September 20, 2023. Please ask your application developer to migrate to a supported platform.
Info: applications using this runtime:
   io.github.daviddesimone.opencloudsaves

To Reproduce
Steps to reproduce the behavior:

1. Run flatpak update

Expected behavior
No warnings.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Linux Flatpak
• Version 0.18.1

Additional context

This runtime is EOL and should be updated. I've never built Flatpak's before, so I'm not sure if it's as simple as just bumping the number in the manifest and testing, but I can try a PR for that.