scripts: Fix flatpak-bisect log

The script was using stdout=subprocess.STDOUT but the Popen
documentation does not mention this as a valid value.

An exception was being thrown when running flatpak-bisect <name> log:
OSError: [Errno 9] Bad file descriptor
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f