sourcegraph/server: Syntect server: "server closed idle connection bug" fix was not applied correctly

Created by: slimsag

In https://github.com/sourcegraph/sourcegraph/issues/2615 we fixed an issue where syntect server would return server closed idle connection errors. Unfortunately, since we applied the fix to only our Dockerfile for that service and I forgot to suggest applying it to the environment in sourcegraph/server:

https://sourcegraph.com/github.com/sourcegraph/sourcegraph@cdedd0e83a68a314f67d53e261209e272d787735/-/blob/cmd/server/shared/shared.go#L147

The issue has remained there undiscovered until now. :/

Reported by https://app.hubspot.com/contacts/2762526/company/554338610