Does Orisa's Halt! displace a Bastion in Sentry configuration?

Yes, in PTR it does but it's not meant to and it has been logged as a bug

https://us.battle.net/forums/en/overwatch/topic/20753187460

The pull effect from Halt! can unintentionally drag immune heroes, like Bastion in Siege mode, or Mei while she is inside Cryo-Freeze.

I'm assuming Siege mode means Sentry mode and is a misspell on the part of Blizzard.

Yes, it moves Bastion, but like Zarya's ult, it does not change him out of sentry mode.