This Cl changes the default acos test value so it equals `cos(.25)`
instead of `cos(.5)`. The `.5` result was slightly different on
various machines.
Bug: tint:1581
Change-Id: I768141ae87a63b2c35ec4d61eb030edad77e11e4
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/108863
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>