Put back CI=true when running on CI

[amaury1093]

In #896, I added CI=false in the yarn build:extension step: https://github.com/paritytech/substrate-light-ui/pull/896/files#diff-b9cfc7f2cdf78a7f4b91a753d10865a2R22

This is to avoid a known webpack issue around dynamic requires, introduced by using wasm, see for example wasm-bindgen/wasm-pack#822:

Critical dependency: the request of a dependency is an expression

It's really not critical, and everything works with this CI=false. Just a reminder issue.