Downgrade react and react-dom to 19.0.0-rc.0 (#67788)

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### What?

Fix potential production compatibility problems with reproduction
templates

With the possibility of introducing `npx` problems (like what @samcx
[fixed](#66301)) or other dev
problems (like what [I
reported](#67783))

### Why?

According to @eps1lon, versions other than `19.0.0-rc.0` can break in
production

### How?

Downgrade `react` and `react-dom` in App Router reproduction template to
`19.0.0-rc.0`

Author: karlhorky

examples/reproduction-template/package.json

@@ -7,8 +7,8 @@
   },
   "dependencies": {
     "next": "canary",
-    "react": "19.0.0-rc-6f23540c7d-20240528",
-    "react-dom": "19.0.0-rc-6f23540c7d-20240528"
+    "react": "19.0.0-rc.0",
+    "react-dom": "19.0.0-rc.0"
   },
   "devDependencies": {
     "@types/node": "20.12.12",