Fix/next info experimental analyze with graph css chunking (#95542)
Fixes: https://github.com/vercel/next.js/issues/95530
- Make sure analyze sets `process.env.TURBOPACK ??= '1'`
- Gate the validation - do not run it for `next info` phase
To be honest, I am not sure about the unit test, I had also modified
`test/e2e/next-analyze/next.config.js` to include the `cssChunking`
graph option, but didn't feel like it was the right direction.
Just minimally added a unit test for the regression.