Add GNOME 50 support in metadata.json

[freemans32]

Added GNOME 50 to the supported shell versions in metadata.json.

Tested on Ubuntu 26.04 LTS beta with GNOME 50.

[bendavis78]

This is not able to build from src

$ npm i
npm error code ERESOLVE
npm error ERESOLVE unable to resolve dependency tree
npm error
npm error While resolving: tilingshell@17.3
npm error Found: esbuild@0.25.12
npm error node_modules/esbuild
npm error   dev esbuild@"^0.25.10" from the root project
npm error
npm error Could not resolve dependency:
npm error peer esbuild@">=0.27.3" from esbuild-sass-plugin@3.7.0
npm error node_modules/esbuild-sass-plugin
npm error   dev esbuild-sass-plugin@"^3.3.1" from the root project
npm error
npm error Fix the upstream dependency conflict, or retry this command with --force or --legacy-peer-deps to accept an incorrect (and potentially broken) dependency resolution.
npm error
npm error
npm error For a full report see:
npm error /home/ben/.npm/_logs/2026-04-12T14_16_39_191Z-eresolve-report.txt
npm error A complete log of this run can be found in: /home/ben/.npm/_logs/2026-04-12T14_16_39_191Z-debug-0.log

[Xake]

What does this PR add that is not already in https://github.com/domferr/tilingshell/commits/v18.0/ ?