Fix flag workflows

Several flags are marked as `workflow: PREBUILT` when they should be
`workflow: MANUAL` or `workflow: LAUNCH`.

Bug: None
Ignore-AOSP-First: part of internal process
Test: manual, TH
Merged-In: Ib7874c34ef4264fc31d1222f124aab7f503a6a33
Change-Id: Ib7874c34ef4264fc31d1222f124aab7f503a6a33