Fix experimental undici warning (vercel#41077)

Fixes: https://vercel.slack.com/archives/C03KAR5DCKC/p1664581332858249

## Bug

- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

packages/next/server/config.ts

@@ -49,12 +49,16 @@ const experimentalWarning = execOnce(
 
 export function setHttpClientAndAgentOptions(options: NextConfig) {
   if (semverGte(process.version, '16.8.0')) {
-    if (semverGte(process.version, '18.0.0')) {
+    if (
+      options.experimental?.enableUndici &&
+      semverGte(process.version, '18.0.0')
+    ) {
       Log.warn(
         '`enableUndici` option is unnecessary in Node.js v18.0.0 or greater.'
       )
+    } else {
+      ;(global as any).__NEXT_USE_UNDICI = options.experimental?.enableUndici
     }
-    ;(global as any).__NEXT_USE_UNDICI = options.experimental?.enableUndici
   } else if (options.experimental?.enableUndici) {
     Log.warn(
       '`enableUndici` option requires Node.js v16.8.0 or greater. Falling back to `node-fetch`'

test/e2e/prerender.test.ts

@@ -2428,6 +2428,11 @@ describe('Prerender', () => {
       expect(next.cliOutput).not.toContain('Failed to update prerender cache')
     })
 
+    it('should not have experimental undici warning', async () => {
+      await waitFor(1000)
+      expect(next.cliOutput).not.toContain('option is unnecessary in Node.js')
+    })
+
     it('should not have attempted sending invalid payload', async () => {
       expect(next.cliOutput).not.toContain('argument entity must be string')
     })