fix: upgrade to React 19 in CI workflow

The test workflow was using React 18 which doesn't have the same
renderToReadableStream API as React 19. Local development uses React 19,
causing a mismatch that led to test failures in CI.

Updated the workflow to install react@19 and react-dom@19 to match the
local development environment and ensure renderToReadableStream works
correctly in the bundled server.js.

Author: GSMLG-BOT

.github/workflows/test.yml

@@ -50,7 +50,7 @@ jobs:
           mix deps.get
 
       - name: Install JavaScript dependencies
-        run: bun install react@18 react-dom@18 react-markdown remark-gfm
+        run: bun install react@19 react-dom@19 react-markdown remark-gfm
 
       - name: Run tests
         run: mix test