Reflip BUILDER_EXTRAS_OVERRIDE to true in main

An error with the automerger boundary between udc* and main caused
changes that had RESTRICT AUTOMERGE to still get merged into main from
udc. Change ag/24622342 was merged into main, even though we wanted the
flag to stay flipped to true in main for additional soak. This change
flips it back to true.

Bug: 280783617
Test: See original code submission that included this flag
Change-Id: I84fd8fbdca92945cd74ee705061f2b8a9b4934ec