Make tests' event capsule flag clientValidated as boolean

EventLogging treats clientValidated as boolean, and meta's
EventCapsule [1] has it as boolean too. So we also set it to boolean
for the tests' event capsule, to make tests pass on HHVM.

[1] https://meta.wikimedia.org/w/index.php?title=Schema:EventCapsule&oldid=8326736

Bug: T78680
Change-Id: I7172e8c7b0b99830cb913e6a1f9edf6ab9891261