feat(depot-scanner): forward non-processed stderr output r/3388

previously, depot-scanner swallowed/ignored all non-processed
stderr output of nix-instantiate, which makes diagnosing
failures of nix-instantiate (e.g. failed with exit status 1)
difficult. This commit fixes that by always forwarding
the remaining stderr messages.

Example previous error message:

  panic: nix-instantiate failed: exit status 1

  goroutine 1 [running]:
  main.main()
	/nix/store/8vb2j13bd7j5ipl7dhsnwvgr7nrrsqsi-main.go:160 +0xeb4

Example new error message:

  nix-inst> error: unrecognised flag '--trace-file-access'
  nix-inst> Try '/run/current-system/sw/bin/nix-instantiate --help' for more information.
  panic: nix-instantiate failed: exit status 1

  goroutine 1 [running]:
  main.main()
	/nix/store/qy7v79a3harddirzmc0432vbzqhyf91i-main.go:165 +0xeb4

Change-Id: I666f3490fc648f77a5384b95edd74f6115f7920d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4553
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

0 files changed, 0 insertions, 0 deletions