github ci node-versions: drop 12.x (#4017)
github ci node-versions: drop 12.x (#4017)

Summary:
Node 12 LTS support ended on 30 April 2022. Dropping it from `.github/ci.yml`. Doing this to unblock [https://github.com/facebook/relay/issues/4016](https://github.com/facebook/relay/pull/4016).

Partly addresses https://github.com/facebook/relay/issues/3883.

I tried adding Node 18.x but ran into `ERR_OSSL_EVP_UNSUPPORTED` with webpack and upgrading webpack seemed non-trivial so I decided to skip that part for now.

Pull Request resolved: https://github.com/facebook/relay/pull/4017

Test Plan:
Imported from GitHub, without a `Test Plan:` line.

**Static Docs Preview: relay**
|[Full Site](https://our.intern.facebook.com/intern/staticdocs/eph/D37922253/V4/relay/)|

|**Modified Pages**|

Reviewed By: kassens

Differential Revision: D37922253

Pulled By: voideanvalue

fbshipit-source-id: 1bf2df842d32febd6eded68d9d19f9b10bed1b7f

facebook/relay,xuorig/relay,facebook/relay,facebook/relay,xuorig/relay,facebook/relay,xuorig/relay,facebook/relay,xuorig/relay,xuorig/relay,facebook/relay,xuorig/relay