fix: follow the upstream review of the react-router 8.4.0 patch

[Mheaus]

Updates patches/react-router@8.4.0.patch to match the latest commit of remix-run/react-router#15612:

• When an enqueue in writeRSCStream fails, its finally releases the reader. stop() could then not cancel the RSC stream, so the RSC render kept running for nothing (no crash). stop() now calls rscStream.cancel() when the stream is no longer locked.
• In production the RSC stream is a tee() branch, and its cancel waits for the other branch. stop() now unblocks flush() before it cancels the RSC stream. Before this, an abort during flush() kept the response open until the RSC render ended.

Verification on the demo production build, with requests that the client aborts after 1–30 ms:

• 300 requests, one at a time: 0 stops;
• 1,000 requests, 20 in parallel: 0 stops, no error in the log.