Reduce cts pressure test notifs sent per app

Reduces the number of notifications sent per app in the cts pressure
test to 40 (producing 320 notifications). This is above the threshold at
which we'd see Binder transaction failures (so should still serve as a
sufficient test), but should help reduce some of the memory pressure we
see on devices with less memory.

Bug: 322645812
Test: atest
Change-Id: I42fe52104409c8d313de362cb83cb261f3c6e122