[code] fix installing extensions in workspace based on postgres image

[akosyakov]

What it does

• fix [code] .gitpod.yml extensions not being installed in VS Code #4460: it is more a work around to make VS Code work when workspaces are based on postgres image. For some reason Node.js process detecting shell env hangs because of stderr although we read everything from it. See child process hangs indefinitely nodejs/node#39072 We don' really need sterr pipe in this case, so I ignore it: gitpod-io/openvscode-server@bd7b462

How to test

Start following workspaces and check that eventually extensions get installed. It can take a while. It maybe that even frontend timeout and you need to reload the page.

https://ak-code-extensions.staging.gitpod-dev.com/#https://github.com/KushagraSinha2002/Resourceium
https://ak-code-extensions.staging.gitpod-dev.com/#https://github.com/connectiveproject/connective

[JanKoehnlein]

LGTM