ci: disable output detection for pre-exit log push

Created by: davejrt

Removes terminal autodetection as this is buggy with buildkite and the moby/term lib we use

Test plan

No more getwinsize errors:

️ Uploading logs	0s
	Fetching logs for https://buildkite.com/sourcegraph/sourcegraph/builds/152630 ...
	Pushing to Loki instance at "logs-prod-us-central1.grafana.net"
	Pushed 379 entries from 1 streams to Loki