chore: use npm info to figure out react version needed for canary instead of hardcoding it

Author: pieh

Diff for: tests/utils/next-version-helpers.mjs

@@ -4,12 +4,11 @@ import { readFile, writeFile } from 'node:fs/promises'
 
 import fg from 'fast-glob'
 import { gte, satisfies, valid } from 'semver'
+import { execaCommand } from 'execa'
 
 const FUTURE_NEXT_PATCH_VERSION = '14.999.0'
 
 const NEXT_VERSION_REQUIRES_REACT_19 = '14.3.0-canary.45'
-// TODO: Update this when React 19 is released
-const REACT_19_VERSION = '19.0.0-rc-1eaccd82-20240816'
 const REACT_18_VERSION = '18.2.0'
 
 /**
@@ -97,8 +96,17 @@ export async function setNextVersionInFixture(
           return
         }
         packageJson.dependencies.next = version
+
+        const { stdout } = await execaCommand(
+          `npm info next@${resolvedVersion} peerDependencies --json`,
+          { cwd },
+        )
+
+        const nextPeerDependencies = JSON.parse(stdout)
+
         if (updateReact && nextVersionRequiresReact19(checkVersion)) {
-          const reactVersion = operation === 'update' ? REACT_19_VERSION : REACT_18_VERSION
+          const reactVersion =
+            operation === 'update' ? nextPeerDependencies['react'] : REACT_18_VERSION
           packageJson.dependencies.react = reactVersion
           packageJson.dependencies['react-dom'] = reactVersion
         }